Loan current carrying value Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process Classes of notes Debt Instrument, Classes Of Notes, Number Debt Instrument, Classes Of Notes, Number Margin, asset Derivative Asset, Subject to Master Netting Arrangement, Collateral, Obligation to Return Cash, Offset Against Derivative Asset Award Timing Predetermined Award Timing Predetermined [Flag] Amortization of tax credit investments Investment Program, Proportional Amortization Method, Applied, Amortization Expense Entity File Number Entity File Number Additional Paid in Capital Additional Paid-in Capital [Member] Impaired loans with an allowance recorded Collateral Dependent Loans, Allowance Allowance for credit loss on collateral dependent loans. Investment-related tax credit Investment Program, Proportional Amortization Method, Elected, Income Tax Credit Reclassification adjustment for gain on sale of AFS securities included in income, net of tax effect of $12.7 and $0.5, respectively Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Tabular List, Table Tabular List [Table Text Block] Transfers of OREO properties to premises and equipment, net Other Real Estate, Transfers Other Real Estate, Transfers Valuation adjustments Other Real Estate, Valuation Adjustments Recent accounting pronouncements and Recently adopted accounting guidance New Accounting Pronouncements, Policy [Policy Text Block] Construction and land development Construction And Land Development [Member] Construction and land development. Estimated Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Measurement Basis [Axis] Measurement Basis [Axis] Realization of cash flows Realization of cash flows Realization of cash flows Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Revenue from Contracts with Customers Revenue from Contract with Customer [Text Block] Financing Receivable Portfolio Segment [Domain] Financing Receivable Portfolio Segment [Domain] Recoveries Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Recovery Derivative liability, collateral, right to reclaim cash, offset Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Offset Restricted stock, performance stock units, and other grants, net (shares) Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Qualifying debt Qualifying Debt Including the current and noncurrent portions, carrying value as of the balance sheet date of junior subordinated debt owed to unconsolidated subsidiary trusts and subordinated debt. Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets. Deposit costs Non-Interest Expense Deposit Costs [Member] Non-Interest Expense Deposit Costs Securities held to maturity, After one year through five years, Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year One through Five Adjustment to Compensation, Amount Adjustment to Compensation Amount Percent of commercial real estate related loans Concentration Risk, Percentage Other assets acquired through foreclosure, measurement input Repossessed Assets, Measurement Input Repossessed Assets, Measurement Input Other assets Increase (Decrease) in Other Operating Assets Principles of consolidation Consolidation, Policy [Policy Text Block] Stock-based compensation Share-Based Payment Arrangement, Noncash Expense Employee Stock Option Share-Based Payment Arrangement, Option [Member] Commercial Segment Commercial Segment [Member] Commercial Segment Loans HFI Collateral Dependent Loans, Net of Allowance Collateral dependent loans, net of allowance for credit loss. Grantee Status [Domain] Grantee Status [Domain] Dividends paid Dividends, Common Stock, Cash Total Western Alliance stockholders’ equity Equity, Attributable to Parent Measurement Frequency [Axis] Measurement Frequency [Axis] Securities held to maturity, After five years through ten years, Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 5 through 10 Debt Securities, Available-for-Sale [Table] Debt Securities, Available-for-Sale [Table] Change in fair value of trading securities, loans HFS, mortgage servicing rights, and related derivatives Increase (Decrease) In Loans Held-For-Sale, Trading Securities, Mortgage Servicing Rights, And Derivatives Increase (Decrease) In Loans Held-For-Sale, Trading Securities, Mortgage Servicing Rights, And Derivatives Other comprehensive income (loss), net: Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Common stock, shares authorized (shares) Common Stock, Shares Authorized Long-term FHLB Advance, Issued January 30, 2026 Long-term FHLB Advance, Issued January 30, 2026 [Member] Long-term FHLB Advance, Issued January 30, 2026 Financial assets Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Fair Value, Recurring Fair Value, Recurring [Member] Derivative Liabilities Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value Non-agency Loans Insured or Guaranteed by non-US Government Authorities [Member] Cover [Abstract] Warehouse Agreement Borrowings Warehouse Agreement Borrowings [Member] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Maximum Maximum [Member] Amortized cost Amortized cost HTM Debt Securities, Held-to-Maturity, Excluding Accrued Interest, before Allowance for Credit Loss Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Wholesale deposits Deposits, Wholesale Total Fair Value Debt Securities, Available-for-Sale, Unrealized Loss Position Securities available for sale, After ten years, Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 Restricted Stock Restricted Stock [Member] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Unrealized gains Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss) Investment-related Liabilities Investment-related Liabilities Debt Instrument [Line Items] Debt Instrument [Line Items] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Credit Linked Notes Maturing July 2059 Credit Linked Notes Maturing July 2059 [Member] Credit Linked Notes Maturing July 2059 Carrying value of debt securities sold Debt Securities, Sold During Period, Carrying Value Debt Securities, Sold During Period, Carrying Value Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Series B Preferred Stock Series B Preferred Stock [Member] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Other Assets Other Assets [Member] Unrealized gain on junior subordinated debt, net of tax effect of $(0.3) and $(0.4), respectively Changes included in OCI, net of tax Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Loans held-for-sale, fair value Fair Value, Option, Loans Held as Assets Fair Value, Option, Loans Held as Assets Income before provision for income taxes Income (loss) before provision for income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Conditional prepayment rate Schedule of Sensitivity Analysis of Fair Value, Discount Rate Change [Abstract] Schedule of Sensitivity Analysis of Fair Value, Discount Rate Change Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Debt securities, held to maturity, Mortgage backed securities, Estimated Fair Value Debt Securities, Held-to-Maturity, Maturity, without Single Maturity Date, Fair Value Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Total interest expense Interest expense Interest Expense, Operating Unsettled purchase of investment securities Investments Purchased, Not Yet Settled Investments Purchased, Not Yet Settled Letter of Credit Letter of Credit [Member] Insurance General Insurance Expense Individually Evaluated for Credit Loss Financing Receivable, Allowance for Credit Loss, Individually Evaluated Document Fiscal Period Focus Document Fiscal Period Focus Goodwill and intangible assets, net Intangible Assets, Net (Including Goodwill) Award Timing Method Award Timing Method [Text Block] Total Nonaccrual Total Nonaccrual Financing Receivable, Excluding Accrued Interest, Nonaccrual Securities available for sale Total, Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, after Allowance for Credit Loss Award Type [Axis] Award Type [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Realization of cash flows Servicing Asset at Fair Value, Other Changes in Fair Value Charge-off Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Loan Sold Trading Symbol Trading Symbol Entity Address, City or Town Entity Address, City or Town Class of Financing Receivable [Axis] Class of Financing Receivable [Axis] Aggregate grant date fair value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value, Aggregate Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value, Aggregate Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Income Statement Location [Domain] Statement of Income Location, Balance [Domain] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Other liabilities Other Liabilities Segment Other Liabilities Segment Entity Emerging Growth Company Entity Emerging Growth Company Depositary Shares Depositary Shares [Member] Depositary Shares Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Unfunded Loan Commitment Unfunded Loan Commitment [Member] Unamortized Debt Issuance Costs Debt Issuance Costs, Net Total change in fair value of derivatives Derivative, Gain (Loss) on Derivative, Net Gross proceeds Sale of Stock, Consideration Received on Transaction, Gross Sale of Stock, Consideration Received on Transaction, Gross Modified loans Financing Receivable, Excluding Accrued Interest, Modified, Accumulated Total non-interest income Non-interest income Noninterest Income Net gain on residential mortgage loans HFS Gain (Loss) on Sales of Loans, Net Gross unrealized (losses) Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss Non-interest expense: Noninterest Expense [Abstract] Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Cash and due from banks Cash and Due from Banks Provision for and change in estimate of liability for losses under representations and warranties, net Provision for and change in estimate of liability for losses under representations and warranties Provision for and change in estimate of liability for losses under representations and warranties Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Servicing Fee Rate Servicing Fee Rate [Member] Servicing Fee Rate Loans Past Due 90 Days or More and Still Accruing Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing UPB, option, loans held as assets, current through 89 days Fair Value, Option, Loans Held as Assets, UPB, Current Through 89 Days Fair Value, Option, Loans Held as Assets, UPB, Current Through 89 Days Loss on sale of loan Gain (Loss) on Sale of Financing Receivable Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Cumulative basis adjustment during period Hedged Asset, Fair Value Hedge, Portfolio Layer Method, Hedged Layer, Fair Value, Cumulative Increase (Decrease) During Period Hedged Asset, Fair Value Hedge, Portfolio Layer Method, Hedged Layer, Fair Value, Cumulative Increase (Decrease) During Period Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] Net proceeds from issuance of equity by a subsidiary Proceeds from Issuance or Sale of Equity Securities held to maturity, After one year through five years, Estimated Fair Value Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Pledged Status [Domain] Pledged Status [Domain] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Income tax expense Income tax expense (benefit) Income Tax Expense (Benefit) Period of basis point spread Debt Instrument, Basis Spread on Variable Rate Other assets Other Assets Gain on sales of investment securities Gain (Loss) On Sales Of Investment Securities Gain (Loss) On Sales Of Investment Securities Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Balance, beginning of period Balance, end of period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Loan servicing expenses Expense Related to Distribution or Servicing and Underwriting Fees Servicing asset, measurement input Servicing Asset, Measurement Input Preferred stock, shares issued (shares) Preferred Stock, Shares Issued Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Hedging Relationship [Axis] Hedging Relationship [Axis] MSR UPB of underlying loans MSR Sales, UPB of underlying loans The unpaid principal balance of loans underlying sales of mortgage servicing rights Securities held to maturity, Due in one year or less, Estimated Fair Value Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Unrealized gain (loss) on junior subordinated debt, tax effect Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, Tax Interest receivable, allowance Allowance for Credit Loss, Receivable, Other, Current Credit quality deterioration, purchase Financing Receivable, Purchased with Credit Deterioration, Amount at Purchase Price Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Dividends on preferred stock Preferred Stock Dividends, Income Statement Impact Other income Noninterest Income, Other Operating Income Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Share Repurchase Program [Member] Share Repurchase Program [Member] Share Repurchase Program Borrowings and qualifying debt Borrowings and Qualifying Debt Total borrowings and qualifying debt. Cumulative fair value hedging adjustment Financing Receivable, Increase (Decrease) From Cumulative Fair Value Hedging Adjustment Financing Receivable, Increase (Decrease) From Cumulative Fair Value Hedging Adjustment Other fees Other Fees [Member] Other Fees Derivative asset, collateral, obligation to return cash, offset Derivative Asset, Subject to Master Netting Arrangement, Collateral, Obligation to Return Cash, Offset Against Derivative Asset, Net of Adjustments Derivative Asset, Subject to Master Netting Arrangement, Collateral, Obligation to Return Cash, Offset Against Derivative Asset, Net of Adjustments Scheduled cash collections Scheduled Cash Collections [Member] Scheduled Cash Collections [Member] Net cash used in operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Total amount Fair Value Disclosure, off-Balance-Sheet Risks, Face Amount, Liability Proceeds from sales Proceeds from Sale of Debt Securities, Available-for-Sale Investment securities - AFS, at fair value; amortized cost of $19,343 at March 31, 2026 and $19,303 at December 31, 2025 Fair value Securities available for sale Total, Estimated Fair Value AFS Debt Securities, Available-for-Sale, Excluding Accrued Interest Sales and payments Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Hotel franchise finance Hotel franchise finance [Member] Hotel franchise finance [Member] Preferred stock, par value (dollars per share) Preferred Stock, Par or Stated Value Per Share Subsequent Event Subsequent Event [Member] Net interest income Net interest income Interest Income (Expense), Operating Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Tax-exempt Nontaxable Municipal Bonds [Member] Derivative Liabilities Derivative liability, fair value Derivative Liability, Subject to Master Netting Arrangement, before Offset Equity Components [Axis] Equity Components [Axis] Three years before current fiscal year Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year Standby letters of credit Standby Letters of Credit [Member] Loans and Leases Receivable Disclosure [Table] Loans and Leases Receivable Disclosure [Table] Transfers of loans HFI to HFS, net of fair value loss adjustment Loan And Lease, Transfer From Held-In-Portfolio To Held-For-Sale, Net Of Fair Value Adjustments Loan And Lease, Transfer From Held-In-Portfolio To Held-For-Sale, Net Of Fair Value Adjustments Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Realized loss (gain) on sale of AFS securities included in income, tax effect Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Reportable segments Number of Reportable Segments Interchange fees Interchange Fees [Member] Interchange Fees Entity Address, State or Province Entity Address, State or Province Classified Substandard [Member] Total interest income Interest income Interest and Dividend Income, Operating Special mention Special Mention [Member] Financial Asset, Period Past Due [Domain] Financial Asset, Aging [Domain] Dividends paid to common stockholders Dividends, Common Stock Mortgage servicing rights Servicing Asset Other time deposits, brokered Time Deposits, $250,000 or More, Retail-Brokered Time Deposits, $250,000 or More, Retail-Brokered Individual: Individual [Axis] Loans held for sale Loans held for sale [Member] Loans held for sale Cash, cash equivalents, and investment securities Cash, Cash Equivalents and Investment Securities Cash, Cash Equivalents and Investment Securities Deposit Liability [Table] Deposit Liability [Table] Goodwill weighting assigned Goodwill Assigned, Percentage Goodwill Assigned, Percentage Unsecured loan commitments Unsecured Loan Commitments Unsecured loan commitments. Securities available for sale, Mortgage backed securities, Amortized Cost Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost Qualifying debt Qualifying Debt [Member] Qualifying Debt Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Payments on long-term debt Repayments of Long-Term Debt Entity Interactive Data Current Entity Interactive Data Current Warehouse Borrowings Warehouse Agreement Borrowings Weighted average rate on FHLB advances, short-term Federal Home Loan Bank, Advances, Weighted Average Interest Rate, Maturing in Next 12 Rolling Months Financing Receivable, Troubled Debt Restructuring [Line Items] Financing Receivable, Modified [Line Items] Dividends and other Dividend Income, Securities, Operating, Taxable Provision for (recovery of) credit losses Debt Securities, Held-to-Maturity, Excluding Accrued Interest, Credit Loss Expense (Reversal) Interest income: Interest and Dividend Income, Operating [Abstract] Held-to-Maturity Securities Held-to-Maturity Securities [Member] Total non-interest expense Noninterest Expense Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Land area of site (in acres) Area of Land Payment Delay Payment Deferral [Member] Deposits Interest Expense, Deposits Unrealized Losses and Fair Value of Investment Securities in Continuous Unrealized Loss Position Held To Maturity Securities And Available For Sale Continuous Unrealized Loss Position Table [Table Text Block] Held to maturity securities and available-for-sale continuous unrealized loss position. Non-interest income: Noninterest Income [Abstract] Accrued interest payable Interest Payable, Current Entity Central Index Key Entity Central Index Key PEO Name PEO Name Realized (loss) gain on derivatives Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Mortgage finance Mortgage Finance [Member] Mortgage finance[Member] Credit Quality Indicators Financing Receivable Credit Quality Indicators [Table Text Block] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Beginning balance Ending balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Non-interest bearing Noninterest-Bearing Deposit Liabilities Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Loans HFI, measurement input Collateral Dependent Loans, Measurement Input Collateral Dependent Loans, Measurement Input Schedule of Fair Value of the Company's Derivative Instruments Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Class of Stock [Domain] Class of Stock [Domain] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Cumulative Fair Value Hedging Adjustment Cumulative basis adjustment, including carrying value of hedged items increase (decrease) Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) 20% change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Conditional Prepayment Rate, 20% Change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Conditional Prepayment Rate, 20% Change Value of foreclosed residential real estate properties Real Estate Acquired Through Foreclosure Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Address Line One Entity Address, Address Line One Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Restricted stock surrendered (shares) Shares withheld (shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Nature of operations Nature Of Operation Policy [Policy Text Block] Nature of operation. Lifetime liquidation probability Lifetime Liquidation Probability [Member] Lifetime Liquidation Probability Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Derivative Liabilities Fair Value Hedge Liabilities Long-term FHLB Advance, Issued November 26, 2025 Long-term FHLB Advance, Issued November 26, 2025 [Member] Long-term FHLB Advance, Issued November 26, 2025 Off-Balance-Sheet, Credit Loss, Liability [Roll Forward] Off-Balance-Sheet, Credit Loss, Liability [Roll Forward] Internal Credit Assessment [Domain] Internal Credit Assessment [Domain] Loans and Leases Receivable Disclosure [Line Items] Loans and Leases Receivable Disclosure [Line Items] Derivatives and Hedging Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] 10% change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Cost To Service, 10% Change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Cost To Service, 10% Change Unrated Corporate Credit Quality Indicator Unrated [Member] Corporate Credit Quality Indicator Unrated [Member] [Member] Fair Value as of Grant Date Award Grant Date Fair Value Four years before current fiscal year Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year Salaries and employee benefits Labor and Related Expense Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Unpaid principal balance of mortgage loans serviced for others Continuing Involvement with Transferred Financial Assets, Principal Amount Outstanding Granted (shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Consumer Related Segment Consumer Related Segment [Member] Consumer Related Segment Derivative Assets Fair Value Hedge Assets Document Quarterly Report Document Quarterly Report Less Than Twelve Months, Fair Value Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Modified loans current with contractual payments Financing Receivable, Excluding Accrued Interest, Modified, Accrual Status Financing Receivable, Excluding Accrued Interest, Modified, Accrual Status Deposits Deposit Liabilities Disclosures [Text Block] Deferred income taxes Deferred Income Taxes and Tax Credits Income from bank owned life insurance Bank Owned Life Insurance Income Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Summary of Recorded Investment in Nonaccrual Loans and Loans Past Due 90 Days Still Accruing Interest by Loan Class Financing Receivable, Nonaccrual [Table Text Block] Loans: Loans and Leases Receivable, Net Amount [Abstract] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Accrued interest receivable Accrued Investment Income Receivable Loans Insured or Guaranteed by Government Authorities [Domain] Loans Insured or Guaranteed by Government Authorities [Domain] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Unsecured letters of credit Unsecured Letters Of Credit Unsecured letters of credit. Non-PEO NEO Non-PEO NEO [Member] Preferred stock dividend rate Preferred Stock, Dividend Rate, Percentage Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Gross unrealized gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Gain (loss) on MSR sales Servicing Asset at Fair Value, Period Increase (Decrease) Award Type [Domain] Award Type [Domain] Noncontrolling interest in subsidiary Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Properties repossessed Other Real Estate, Foreclosed Assets, and Repossessed Assets, Number Of Properties Repossessed Other Real Estate, Foreclosed Assets, and Repossessed Assets, Number Of Properties Repossessed Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Compensation Amount Outstanding Recovery Compensation Amount Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Foreign currency contracts Foreign Exchange Contract [Member] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Estimate of Fair Value Measurement Estimate of Fair Value Measurement [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Securities available for sale, After one year through five years, Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] Other Assets Acquired Through Foreclosure Other Assets Disclosure [Text Block] 2030 Time Deposit Maturities, Year Four Financing Receivable, Nonaccrual [Line Items] Financing Receivable, Past Due [Line Items] Securities available for sale, After five years through ten years, Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Collateral-Dependent Loans Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Investments in LIHTC and renewable energy Investment, Proportional Amortization Method, Elected, Amount Banking service charges and fees Banking Service Charges And Fees [Member] Banking Service Charges And Fees Financial Instruments [Domain] Financial Instruments [Domain] Securities held to maturity, After ten years, Estimated Fair Value Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Purchases and additions Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Award Date [Domain] Award Date [Domain] Performance Shares Performance Shares [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Change in fair value Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss) Real Estate Collateral Real Estate Collateral [Member] Real Estate Collateral [Member] Minimum Minimum [Member] Net interest income after provision for credit losses Net interest income (expense) after provision for credit losses Interest Income (Expense), after Provision for Loan Loss FRB Federal Reserve Bank Advances [Member] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Company Selected Measure Name Company Selected Measure Name Fair Value Measurement [Domain] Fair Value Measurement [Domain] Summary of Contractual Amounts for Unfunded Commitments and Letters of Credit Schedule of Fair Value, off-Balance-Sheet Risks [Table Text Block] Valuation allowance Repossessed Assets, Valuation Allowance Repossessed Assets, Valuation Allowance Investment securities - AFS Investment Securities - AFS [Member] Investment Securities - AFS Other Borrowings Qualifying Debt Debt Disclosure [Text Block] Sale of investment securities Gain (Loss) on Sale of Investments Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Collateral [Domain] Collateral Held [Domain] Stockholders' Equity Note [Abstract] Stockholders' Equity Note [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Portfolio layer method swaps Portfolio Layer Method Swaps [Member] Portfolio Layer Method Swaps Diluted (shares) Weighted average shares - diluted (shares) Weighted Average Number of Shares Outstanding, Diluted Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Derivative [Table] Derivative [Table] Proceeds from bank owned life insurance, net Proceeds from Life Insurance Policy Entity Small Business Entity Small Business Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity [Abstract] Preferred stock, shares outstanding (shares) Preferred Stock, Shares Outstanding Document Transition Report Document Transition Report Securities available for sale, After one year through five years, Estimated Fair Value Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Commercial MBS issued by GSEs and GNMA Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member] Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member] Underlying Securities Award Underlying Securities Amount Financing receivable, UPB Fair Value, Option, Loans Held as Assets, UPB Fair Value, Option, Loans Held as Assets, UPB Gross gains Debt Securities, Available-for-Sale, Realized Gain Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date Rollforward by Major Security Type of the ACL on HTM Debt Securities Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Table Text Block] Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Line Items] Income Taxes Income Tax Disclosure [Text Block] Cash and cash equivalents Cash, Cash Equivalents, and Federal Funds Sold Cumulative basis adjustment Hedged Asset, Fair Value Hedge, Portfolio Layer Method, Hedged Layer, Fair Value, Cumulative Increase (Decrease) Payment of contingent consideration Payment for Contingent Consideration Liability, Financing Activities Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Portfolio layer method derivative instruments Hedged Asset, Fair Value Hedge, Portfolio Layer Method, Hedged Layer, Amount Total equity Beginning balance Ending balance Total equity Equity, Including Portion Attributable to Noncontrolling Interest Weighted average price of treasury shares (dollars per share) Shares Acquired, Average Cost Per Share Document Type Document Type Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Earnings Per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Loss Contingencies [Table] Loss Contingencies [Table] FHLB advances Long-Term Federal Home Loan Bank Advances Revolving Loans Amortized Cost Basis, Writeoff Financing Receivable, Excluding Accrued Interest, Revolving, Writeoff Credit linked notes, net Notes Payable Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Subordinated Debentures Maturing June 2031 Subordinated Debentures Maturing June 2031 [Member] Subordinated Debentures Maturing June 2031 Notional Amount, Margin Derivative Netting Adjustments, Notional Amount Derivative Netting Adjustments, Notional Amount Fair value, option, loans held as assets, current through 89 days, aggregate difference Fair Value, Option, Loans Held as Assets, Current Through 89 days, Aggregate Difference Fair Value, Option, Loans Held as Assets, Current Through 89 days, Aggregate Difference 10% change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Conditional Prepayment Rate, 10% Change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Conditional Prepayment Rate, 10% Change Statistical Measurement [Axis] Statistical Measurement [Axis] Other Liabilities Disclosure [Abstract] Other Liabilities Disclosure [Abstract] Share repurchase program authorized amount Share Repurchase Program, Authorized, Amount Servicing Contracts Servicing Contracts [Member] Year before current fiscal year, writeoff Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff Other assets Other Assets Segment Other Assets Segment Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Cash paid for tax withholding on vested restricted stock and other Payment, Tax Withholding, Share-Based Payment Arrangement Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Net income available to common stockholders Net income available to common stockholders Net Income (Loss) Available to Common Stockholders, Basic Entity Information [Line Items] Entity Information [Line Items] Share Repurchase Program [Domain] Share Repurchase Program [Domain] Credit quality deterioration, principal balance Financing Receivable, Purchased with Credit Deterioration, Amount at Par Value Derivative Instruments, Gain (Loss) Derivative Instruments, Gain (Loss) [Table Text Block] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Diluted (dollars per share) Earnings Per Share, Diluted Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Roll Forward] Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Roll Forward] Securities available for sale, After five years through ten years, Estimated Fair Value Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Recoveries Debt Securities, Held-to-Maturity, Excluding Accrued Interest, Allowance for Credit Loss, Recovery Amortized cost basis Financing Receivable, Excluding Accrued Interest, Modified in Period, Amount Dividends paid to preferred stockholders Dividends, preferred stock Dividends, Preferred Stock, Cash Shares issued (shares) Sale of Stock, Number of Shares Issued in Transaction Loans HFS Financing Receivable, Held-for-Sale Treasury stock (shares) Treasury Stock, Common, Shares Consolidation Items [Domain] Consolidation Items [Domain] Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Interest rate Subordinated Borrowing, Interest Rate Additions from loans sold with servicing rights retained Servicing Asset at Fair Value, Additions Term Extension Extended Maturity [Member] Stock repurchase Stock repurchase Stock Repurchased and Retired During Period, Value Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Axis] Proceeds from sales Proceeds from Sale of Equity Securities, FV-NI Number of statutory business trusts Number of Statutory Business Trusts Formed or Acquired Number of Statutory Business Trusts Formed or Acquired Reciprocal deposits Reciprocal Deposits The aggregate amount of all reciprocal deposits, including CDARS and ICS 2027 Time Deposit Maturities, Year One Income taxes, net Income Taxes Paid, Net Commitments to extend credit Commitments to Extend Credit [Member] Corporate debt securities Corporate Bond Securities [Member] Other non-interest income Other non-interest income [Member] Other non-interest income Unrealized (loss) gain on AFS securities, net of tax effect of $25.1 and $(19.4), respectively OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Derivative asset, measurement input Derivative Asset, Measurement Input Loans HFI, net of deferred fees and costs Loans HFI, net of deferred fees and costs Outstanding balance Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss Aggregate grant date fair value Shares Granted, Value, Share-Based Payment Arrangement, before Forfeiture Dividends paid to noncontrolling interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Expiration Date Trading Arrangement Expiration Date Noncumulative Preferred Stock Noncumulative Preferred Stock [Member] Other Commitments [Domain] Other Commitments [Domain] Gains and Losses from Fair Value Changes Included in Consolidated Statement of Operations Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Table Text Block] Increase (Decrease) in Other Operating Liabilities Increase (Decrease) in Other Operating Liabilities Unrealized gains (losses) on assets measured at fair value, net Equity Securities, FV-NI, Unrealized Gain (Loss) Investment securities - HTM, allowance for credit losses Beginning balance Ending balance Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Excluding Accrued Interest Premises and equipment, net Property, Plant and Equipment, Net Long-term FHLB Advance, Issued October 30, 2025 Long-term FHLB Advance, Issued October 30, 2025 [Member] Long-term FHLB Advance, Issued October 30, 2025 Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Series A Preferred Stock Series A Preferred Stock [Member] Entity Current Reporting Status Entity Current Reporting Status Receivables [Abstract] Receivables [Abstract] Derivative [Line Items] Derivative [Line Items] Purchase of premises, equipment, and other assets, net Payments for (Proceeds from) Productive Assets Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Collateral [Axis] Collateral Held [Axis] Credit Linked Notes Maturing October 2052 Credit Linked Notes Maturing October 2052 [Member] Credit Linked Notes Maturing October 2052 Securities available for sale, Due in one year or less, Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One UPB, op days or more delinquent Fair Value, Option, Loans Held as Assets, UPB, 90 Days or More Past Due Fair Value, Option, Loans Held as Assets, UPB, 90 Days or More Past Due Derivative liability, fair value, gross liability including not subject to master netting arrangement Derivative Liability, Gross Liability Including Not Subject to Master Netting Arrangement Non-EBO Purchased from correspondent seller [Member] Purchased from correspondent sellers or originated in house Derivative liability, subject to master netting arrangement, after offset Derivative Liability, Subject to Master Netting Arrangement, after Offset Financial Instrument [Axis] Financial Instrument [Axis] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Executive Category: Executive Category [Axis] More Than Twelve Months, Gross Unrealized Losses Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Net proceeds from issuance of long-term debt Proceeds from Issuance of Long-Term Debt Current Fiscal Year End Date Current Fiscal Year End Date Less Than Twelve Months, Gross Unrealized Losses Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Total deposits Total deposits Deposits Fair Value, option, loans held as assets, current through 89 days Fair Value, Option, Loans Held as Assets, Current Through 89 Days Fair Value, Option, Loans Held as Assets, Current Through 89 Days Loan acquisition and origination expenses Loan Processing Fee Summary of Loans HFS by Type Summary of Net Gain on Loan Purchase, Origination and Sale Activities on Residential Mortgage Loans Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Aggregated difference, 90 days or more delinquent Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due, Aggregate Difference Derivative Assets Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value Negative NPVs Derivative liabilities Derivative Liability Other expense Other Noninterest Expense Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Loan purchases Financing Receivable, Excluding Accrued Interest, Purchase Loan Restructuring Modification [Axis] Loan Restructuring Modification [Axis] Pass Pass [Member] Proceeds from sale of mortgage servicing rights and related holdbacks, net Proceeds from Sale of Mortgage Servicing Rights (MSR) Derivative asset, not subject to master netting arrangement Derivative Asset, Not Subject to Master Netting Arrangement Servicing advances, net Servicing advances, net Servicing advances, net Total Gross Unrealized Losses Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss Investment securities - equity Equity Securities, FV-NI, Current Weighted average number of common shares outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Schedule of Held-to-Maturity Securities [Line Items] Schedule of Held-to-Maturity Securities [Line Items] FHLB advances Federal Home Loan Bank, Advance, Maturity, Year One Aging of Loan Portfolio by Loan Portfolio Segment Financing Receivable, Past Due [Table Text Block] Interest bearing Interest-Bearing Deposit Liabilities Other Commitments [Table] Other Commitments [Table] Net cash provided by financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Other deposit related costs Deposits, Earnings Credit And Referral Costs, Other Deposits, Earnings Credit And Referral Costs, Other Measure: Measure [Axis] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Restricted stock, performance stock units, and other grants, net Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Stock repurchase program remaining amount Share Repurchase Program, Remaining Authorized, Amount Unrealized holding gains (losses) on SERP Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Derivative asset, subject to master netting arrangement, after offset Derivative Asset, Subject to Master Netting Arrangement, after Offset Entity Tax Identification Number Entity Tax Identification Number Grantee Status [Axis] Grantee Status [Axis] Valuation Technique, Discounted Cash Flow Valuation Technique, Discounted Cash Flow [Member] Effect of Hypothetical Changes in the Fair Value of MSRs Schedule of Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets [Table Text Block] Three years before current fiscal year, writeoff Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff Securities available for sale, Mortgage backed securities, Estimated Fair Value Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value Discount rate Discount Rate [Member] Discount Rate [Member] Interest rate swap, terminated Interest Rate Swap, Terminated [Member] Interest Rate Swap, Terminated Common stock, shares issued (shares) Common Stock, Shares, Issued Residential MBS issued by GSEs and GNMA Mortgage-Backed Security, Issued by US Government-Sponsored Enterprise [Member] Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Charge-offs Debt Securities, Held-to-Maturity, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff Debt Instrument, measurement input Debt Instrument, Measurement Input Loss Contingencies [Line Items] Loss Contingencies [Line Items] Corporate & Other Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] Security Exchange Name Security Exchange Name Change in fair value of loans HFS and trading securities Change in fair value of loans held for sale and trading securities Change in fair value of loans held for sale and trading securities AAA Corporate Credit Quality Indicator Aaa [Member] Corporate credit quality indicator. Loans Held For Sale Loans, Leases and Allowance for Credit Losses Financing Receivables [Text Block] Asset Class [Domain] Asset Class [Domain] Change in fair value Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Statement [Line Items] Statement [Line Items] Carrying value of hedged assets Hedged Asset, Fair Value Hedge Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Subsequent Event [Line Items] Subsequent Event [Line Items] Increase in DTA Increase (Decrease) in Deferred Income Taxes Common Stock Common Stock [Member] Secured borrowings Other Short-Term Borrowings Servicing fee multiple Servicing Fee Multiple [Member] Servicing Fee Multiple Net increase (decrease) in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Dilutive effect of stock award (shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Servicing Asset at Fair Value, Amount [Roll Forward] Servicing Asset at Fair Value, Amount [Roll Forward] Cash dividend per share (dollars per share) Common Stock, Dividends, Per Share, Cash Paid Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Federal funds purchased Federal Funds Purchased Statistical Measurement [Domain] Statistical Measurement [Domain] Debt [Line Items] Debt [Line Items] Debt [Line Items] Amortized cost Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss Interest income associated with loans on nonaccrual status Financing Receivable, Nonaccrual, Interest Income Weighted average interest rate Long-Term Debt, Weighted Average Interest Rate, at Point in Time AA+ to AA- Corporate Credit Quality Indicator Aa Plus To Aa Minus [Member] Corporate credit quality indicator. Common stock (par value $0.0001; 200,000,000 authorized; 112,413,369 shares issued at March 31, 2026 and 112,491,068 at December 31, 2025) and additional paid in capital Common Stocks, Including Additional Paid in Capital Asset Class [Axis] Asset Class [Axis] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Interest rate contracts Interest Rate Swap [Member] Bank owned life insurance Bank Owned Life Insurance Earnings per share: Earnings Per Share, Basic [Abstract] Subordinated debt issuances Subordinated Long-Term Debt, Noncurrent Corporate And Other Segment Corporate And Other Segment [Member] Corporate And Other Segment Nonaccrual with No Allowance for Credit Loss Financing Receivable, Excluding Accrued Interest, Nonaccrual, No Allowance Pledged Status [Axis] Pledged Status [Axis] Restricted stock surrendered Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Gross unrealized (losses) Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] 2026 Time Deposit Maturities, Remainder of Fiscal Year Basic (dollars per share) Earnings Per Share, Basic Tech & innovation Tech & Innovation [Member] Tech & Innovation [Member] Schedule of Derivative Assets at Fair Value Schedule of Derivative Assets at Fair Value [Table Text Block] Award Date [Axis] Award Date [Axis] Excess funds (used) provided Excess Funds Provided by (Used in) Segment Basis Excess Funds Provided by (Used in) Segment Basis Net other comprehensive (loss) income Other comprehensive income, net Net current-period other comprehensive income Other Comprehensive Income (Loss), Net of Tax Warrant exercises Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) Operating Segment Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Total short-term borrowings Short-Term Debt 2031 Time Deposit Maturities, Year Five Nonaccrual with an Allowance for Credit Loss Financing Receivable, Nonaccrual, With Allowance Amount of financing receivable on nonaccrual status with an allowance for credit loss. Revenue, Remaining Performance Obligation, Amount Revenue, Remaining Performance Obligation, Amount Gross unrealized gains Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain Measurement Input Type [Domain] Measurement Input Type [Domain] Assets Measured at Fair Value on Nonrecurring Basis Fair Value Measurements, Nonrecurring [Table Text Block] Charge-offs Charge-offs Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff Net proceeds from sale of loans Proceeds From Sale, Loan, Mortgage, Held-For-Sale, Net Of Loan Basis Proceeds From Sale, Loan, Mortgage, Held-For-Sale, Net Of Loan Basis Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Changes in Fair Value of the Company's MSR Portfolio Schedule of Servicing Assets at Fair Value [Table Text Block] Investment securities Interest Income, Securities, Operating, Taxable Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Accounts and Financing Receivables [Table] Settlement of IRLCs upon acquisition or origination of loans HFS IRLC, Settlements upon Acquisition or Origination IRLC, settlements upon acquisition or origination of loans held for sale Unrealized holding gains (losses) on AFS securities AOCI, Gain (Loss), Debt Securities, Available-for-Sale, without Allowance for Credit Loss, Parent [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Stock-based compensation expense Share-Based Payment Arrangement, Expense Rollforward by Major Security Type of the ACL on AFS Debt Securities Debt Securities, Available-for-Sale, Allowance for Credit Loss [Table Text Block] Early payoff fee income Servicing Assets, Early Payoff Fee Income Servicing Assets, Early Payoff Fee Income Percentage of CRE loans occupied by owners Percentage Of Commercial Real Estate Loans Occupied By Owners Percentage of commercial real estate Loans occupied by owners. Total liabilities and equity Liabilities and Equity Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Available-for-Sale Securities Available-for-Sale Securities [Member] Accounting Policies [Abstract] Accounting Policies [Abstract] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Forward contracts Forward Contracts [Member] Residential EBO Residential - EBO [Member] Residential - Early buy out Treasury Stock Treasury Stock, Common [Member] Current fiscal year Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year Pay vs Performance Disclosure [Line Items] Operating lease liability Operating Lease, Liability Over 90 days Past Due Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Preferred stock, liquidation value (dollars per share) Preferred Stock, Liquidation Preference Per Share Liabilities: Liabilities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Change in unrealized gains for the period Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) Service charges and fees Service Charges And Loan Fees [Member] Service Charges And Loan Fees Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Gain/(Loss) on Hedged Item Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge Time to expiration (in years) Measurement Input, Time To Expiration [Member] Measurement Input, Time To Expiration Two years before current fiscal year Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Five years before current fiscal year, writeoff Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff Comprehensive income attributable to Western Alliance Comprehensive Income (Loss), Net of Tax, Attributable to Parent Measurement Input Type [Axis] Measurement Input Type [Axis] Net loan servicing (loss) revenue Loan servicing fees, net Loan servicing fees, net Name Measure Name Securities available for sale, Due in one year or less, Estimated Fair Value Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Secured Debt Secured Debt [Member] Change in Level 3 Liabilities Measured at Fair Value on Recurring Basis Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Net increase in deposits Increase (Decrease) in Deposits Principal pay downs and maturities Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-Sale Notional amount terminated during period Derivative, Notional Amount, Terminated During Period Derivative, Notional Amount, Terminated During Period Other time deposits Time Deposits, Less than $250,000 The aggregate amount of domestic or foreign time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than $250,000. Third party appraisal Third Party Appraisal [Member] Third Party Appraisal [Member] Futures contracts Future [Member] Total long-term borrowings Long-Term Debt 20% change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Cost To Service, 20% Change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Cost To Service, 20% Change Legal Entity [Axis] Legal Entity [Axis] Total assets Total assets Assets Agency-conforming US Government Agency Insured Loans [Member] External Credit Rating by Grouping [Domain] External Credit Rating by Grouping [Domain] Cash flows from operating activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Financial Asset, Current to 89 Days Past Due Financial Asset, Current to 89 Days Past Due [Member] Financial Asset, Current to 89 Days Past Due Schedule Of Total Earnings Credit And Referral Costs Schedule Of Total Earnings Credit And Referral Costs [Table Text Block] Schedule Of Total Earnings Credit And Referral Costs Proceeds from sales and payments on loans HFS and related securitization activities Proceeds from Sale and Collection, Loan, Held-for-Sale Investment securities - HTM Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss [Abstract] Amortization of net deferred loan fees and net purchase premiums Amortization of Deferred Loan Origination Fees, Net Service charges and fees Service Charges And Loan Fees Service Charges And Loan Fees 2028 Time Deposit Maturities, Year Two Investment securities - HTM, fair value Investment securities - HTM, fair value Debt Securities, Held-to-Maturity, Fair Value Equity warrants Warrants Warrant [Member] Dividends declared per common share (dollars per share) Common Stock, Dividends, Per Share, Declared Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Pull-through rate Pull-through Rate [Member] Pull-through Rate Municipal & nonprofit Municipal and nonprofit [Member] Municipal and nonprofit [Member] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Securities held to maturity, After five years through ten years, Estimated Fair Value Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Cash Settled Stock Units Cash Settled Stock Units [Member] Cash Settled Stock Units Equity warrants Equity Warrants [Member] Equity Warrants Asset Pledged as Collateral Asset Pledged as Collateral [Member] 20% change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Option Adjusted Spread, 20% Change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Option Adjusted Spread, 20% Change Document Information [Table] Document Information [Table] PEO PEO [Member] Transfers from Level 2 to Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Amortized Cost and Fair Value of Investment Securities by Contractual Maturities Investments Classified by Contractual Maturity Date [Table Text Block] Non-cash activities: Noncash Investing and Financing Items [Abstract] Junior Subordinated Debt Junior Subordinated Debt [Member] Demand accounts Interest-Bearing Domestic Deposit, Demand Total Time Deposits Retained Earnings Retained Earnings [Member] Cash, cash equivalents, and restricted cash at beginning of period Cash, cash equivalents, and restricted cash at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income Statement [Abstract] Largest gross exposure (positive derivative NPV) to an individual counterparty Derivative asset Derivative Asset Fair value gain adjustments, net Fair value gain adjustments, net [Member] Fair value gain adjustments, net More Than Twelve Months, Fair Value Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Cash dividend (dollars per share) Preferred Stock, Dividends, Per Share, Cash Paid Interest expense on qualifying debt Interest Expense [Member] Fair Value, Nonrecurring Fair Value, Nonrecurring [Member] Summary of Contractual Maturities for Time Deposits Time Deposit Maturities [Table Text Block] Financing Receivable, Troubled Debt Restructuring [Table] Financing Receivable, Modified [Table] Provision for (recovery of) credit losses Off-Balance-Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal) Investment securities - AFS Estimated Fair Value Debt Securities, Available-for-Sale [Abstract] Net income Net income Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Notional Amount Derivative, Notional Amount Mortgage servicing rights capitalized upon sale of mortgage loans Capitalization Of Mortgage Servicing Rights (MSRs) Capitalization Of Mortgage Servicing Rights (MSRs) Revolving Loans Amortized Cost Basis Financing Receivable, Excluding Accrued Interest, Revolving City Area Code City Area Code Allowances for Credit Losses Financing Receivable, Allowance for Credit Loss [Table Text Block] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Loans HFS, measurement input Loan, Held-for-Sale, Measurement Input Unrealized holding gains (losses) on junior subordinated debt Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member] CRA investments Cra Investments [Member] CRA investments. Junior subordinated debt Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust Cash flows from investing activities: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Total government-insured or guaranteed Loans Insured or Guaranteed by US Government Authorities [Member] Interest receivable Interest Receivable Other non-interest expense Other Noninterest Expense, Segments Other Noninterest Expense, Segments Schedule of Servicing Assets at Fair Value [Table] Servicing Asset at Fair Value, Activity [Table] Transfers of loans HFI to other assets acquired through foreclosure Loan, Transfer From Held In Portfolio To Other Assets Acquired Through Foreclosure Loan, Transfer From Held In Portfolio To Other Assets Acquired Through Foreclosure Remaining receivable balance MSR Loan Sales, Receivable Receivable balance related to holdbacks on sales for pending servicing transfers Other liabilities Other Liabilities Credit Linked Notes Credit Linked Notes [Member] Credit Linked Notes Properties sold Other Real Estate, Number Of Properties Sold Other Real Estate, Number Of Properties Sold Mortgage Servicing Rights Transfers and Servicing of Financial Assets [Text Block] Derivative Assets, Margin Derivative Netting Adjustments, Assets Derivative Netting Adjustments, Assets Number of unconsolidated subsidiaries Number Of Unconsolidated Subsidiaries Number of unconsolidated subsidiaries. Supplemental disclosure: Supplemental Cash Flow Information [Abstract] (Purchase of) proceeds from other investments Purchase (Sale) of Other Investments Purchase (Sale) of Other Investments Other Performance Measure, Amount Other Performance Measure, Amount Collectively Evaluated for Credit Loss Financing Receivable, Allowance for Credit Loss, Collectively Evaluated Other assets acquired through foreclosure Repossessed Assets Credit Concentration Risk Credit Concentration Risk [Member] Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] Derivative Instrument [Axis] Derivative Instrument [Axis] Financial liabilities Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Commercial Real Estate Portfolio Segment Commercial Real Estate Portfolio Segment [Member] Entity [Domain] Entity [Domain] Net cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] BB+ and below Corporate Credit Quality Indicator Bb Plus And Below [Member] Corporate credit quality indicator. Loans Insured or Guaranteed by Government Authorities [Axis] Loans Insured or Guaranteed by Government Authorities [Axis] Held-to-maturity Debt Securities, Held-to-Maturity, Fair Value [Abstract] Interest Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Servicing Assets at Fair Value [Line Items] Servicing Assets at Fair Value [Line Items] Basis of presentation Basis of Accounting, Policy [Policy Text Block] Lender Name [Axis] Lender Name [Axis] Operating lease right of use asset Operating Lease, Right-of-Use Asset Financing receivable, unamortized premium Financing Receivable, Unamortized Purchase Premium (Discount) Effective tax rate Effective Income Tax Rate Reconciliation, Percent Carrying Amount Reported Value Measurement [Member] Equity fund resources Equity fund resources [Member] Equity fund resources Deferred tax valuation allowance Deferred Tax Assets, Valuation Allowance Equity [Abstract] Equity [Abstract] Cost to service Schedule of Sensitivity Analysis of Fair Value, Conditional Prepayment Rate Change [Abstract] Schedule of Sensitivity Analysis of Fair Value, Conditional Prepayment Rate Change Segments Segment Reporting Disclosure [Text Block] Loans transferred with original designation of HFS, operating cash flows Loan and Lease, Transfer from Held-in-Portfolio to Held-for-Sale, Operating Activity Loan and Lease, Transfer from Held-in-Portfolio to Held-for-Sale, Operating Activity Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] U.S. Treasury securities US Treasury Securities [Member] Carrying value of MSRs sold Servicing Asset at Fair Value, Disposals Other Commitments [Line Items] Other Commitments [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Data processing Information Technology and Data Processing Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Accumulated Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Weighted Average Weighted Average [Member] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Unamortized loan fees Financing Receivable, Unamortized Loan Cost (Fee) Loans Receivable Loans Receivable [Member] Volatility Measurement Input, Price Volatility [Member] Deferred tax assets, net Deferred Income Tax Assets, Net Summary of Changes in Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Preferred stock, ownership interest Equity, Preferred Stock, Ownership Interest, Ratio Equity, Preferred Stock, Ownership Interest, Ratio Net proceeds Sale of Stock, Consideration Received on Transaction Commercial and industrial Commercial and industrial [Member] Commercial and industrial loan type Private label residential MBS Residential Mortgage-Backed Securities [Member] Arrangement Duration Trading Arrangement Duration Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Transfers of mortgage-backed securities in settlement of secured borrowings Transfers of mortgage-backed securities in settlement of secured borrowings Transfers of mortgage-backed securities in settlement of secured borrowings Segments [Axis] Segments [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Subordinated Debentures Maturing November 2035 Subordinated Debentures Maturing November 2035 [Member] Subordinated Debentures Maturing June 2030 [Member] [Member] Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Carrying Amounts and Fair Values of Investment Securities Securities Held To Maturity Available For Sale Securities And Securities Measured At Fair Value Table [Table Text Block] Securities held to maturity, available for sale and measured at fair value. Other Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Other Item Stock repurchase (shares) Stock repurchase (shares) Stock Repurchased and Retired During Period, Shares Balance, beginning of period Balance, end of period Conditional commitments Off-Balance-Sheet, Credit Loss, Liability Assets: Assets [Abstract] Credit Facility [Axis] Credit Facility [Axis] Other Contract Other Contract [Member] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Conditional Prepayment Rate Conditional Prepayment Rate [Member] Conditional Prepayment Rate Other Commitments [Axis] Other Commitments [Axis] Legal, professional, and directors' fees Legal Professional And Director Fees The sum of the amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings, fees paid for consulting and professional services and fees paid to directors for service as a member of the board of directors. Debt Instrument [Axis] Debt Instrument [Axis] Fair Value Accounting Fair Value Disclosures [Text Block] Credit Facility [Domain] Credit Facility [Domain] Earnings credits or referral fees Deposits, earnings credit Deposits that earn earnings credits or referral fees. Equity: Equity, Attributable to Parent [Abstract] Loan sales Financing Receivable, Excluding Accrued Interest, Sale Net increase in short-term borrowings Proceeds from Short-Term Debt Vesting percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage Amortized Cost Basis of Loans Modified Financing Receivable, Modified [Table Text Block] Interest rate Debt Instrument, Interest Rate, Stated Percentage 30-59 Days Past Due Financial Asset, 30 to 59 Days Past Due [Member] Recovery of credit losses Debt Securities, Available-for-Sale, Excluding Accrued Interest, Allowance for Credit Loss, Not Previously Recorded Derivative liability, not subject to master netting arrangement Derivative Liability, Not Subject to Master Netting Arrangement Equity capital weighting assigned Equity Capital Assigned, Percentage Equity Capital Assigned, Percentage Derivative Assets Derivative Asset, Subject to Master Netting Arrangement, before Offset Credit Linked Notes Maturing April 2052 Credit Linked Notes Maturing April 2052 [Member] Credit Linked Notes Maturing April 2052 Entity Registrant Name Entity Registrant Name Debt [Table] Debt [Table] Debt [Table] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Other borrowings Interest Expense, Other Proceeds from non-real estate collateral Proceeds from Non-Real Estate Collateral [Member] Proceeds from Non-Real Estate Collateral [Member] Recapture rate Recapture Rate [Member] Recapture Rate Provision for credit losses Provision for (recovery of) credit losses Provision for Loan, Lease, and Other Losses Number of AFS debt securities in an unrealized loss position Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Deposits: Deposits [Abstract] Total Past Due Financial Asset, Past Due [Member] Balance, beginning of period Balance, end of period Fair value of mortgage servicing rights Servicing Asset at Fair Value, Amount Amortization of net discounts for investment securities Accretion (Amortization) of Discounts and Premiums, Investments Purchases Payments to Acquire Equity Securities, FV-NI Company's Borrowings Schedule of Debt [Table Text Block] Net gain on mortgage loan origination and sale activities Net gain on mortgage loan origination and sale activities Net gain on mortgage loan origination and sale activities Fair value adjustments Assets, Fair Value Adjustment, Non-Cash Assets, Fair Value Adjustment, Non-Cash Fair Value, 90 days or more delinquent Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due Restatement Determination Date: Restatement Determination Date [Axis] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity issued by subsidiary Noncontrolling Interest, Increase from Subsidiary Equity Issuance Small Business Administration Small Business Administration [Member] Small Business Administration Preferred stock, rate reset period Preferred Stock, Rate Reset Period Preferred Stock, Rate Reset Period Amounts reclassified from AOCI Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Investments in restricted stock, at cost Restricted Investments Purchases and originations of loans HFS Payment for Origination and Purchase, Loan, Held-for-Sale Time certificates of deposit ($250,000 or more) Time Deposit Liability, above US Insurance Limit Name Trading Arrangement, Individual Name Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Loans HFS Loan, Held-for-Sale, Fair Value Disclosure BBB+ to BBB- Corporate Credit Quality Indicator Bbb Plus To Bbb Minus [Member] Corporate credit quality indicator. Equity warrants, measurement input Warrants and Rights Outstanding, Measurement Input Principal Debt Instrument, Face Amount Deposit Liability [Line Items] Deposit Liability [Line Items] Business development and marketing Business Development Unrealized gain on SERP, tax effect Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Valuation Allowance [Table] Deferred Tax Asset, Valuation Allowance [Table] Forward contracts Forward purchase and sales contracts [Member] Forward purchase and sales contracts Share Repurchase Program [Axis] Share Repurchase Program [Axis] Preferred Stock Preferred Stock [Member] Income (loss) from equity investments Income from Equity Investments Income from equity investments Percentage of LIBOR Percentage Of Basis Spread On Variable Rate Percentage of basis spread on variable rate. Name Awards Close in Time to MNPI Disclosures, Individual Name Collectively Evaluated for Credit Loss Financing Receivable, Collectively Evaluated for Credit Loss A+ to A- Corporate Credit Quality Indicator A Plus To A Minus [Member] Corporate credit quality indicator. Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Other conditional commitments Other Commitment Comprehensive income attributable to noncontrolling interest Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Equity securities carried at fair value Equity Securities, FV-NI, Gain (Loss) [Abstract] Risk participation agreements Risk participation agreements [Member] Risk participation agreements Treasury stock, at cost (3,175,460 shares at March 31, 2026 and 2,981,687 shares at December 31, 2025) Treasury Stock, Value Unrealized (loss) gain on AFS securities, tax effect OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Loans HFI Loans Held-For-Investments [Member] Loans Held-For-Investments Liability Class [Axis] Liability Class [Axis] Segments [Domain] Segments [Domain] Income Statement Location [Axis] Statement of Income Location, Balance [Axis] Fair value gain adjustments, net Assets, Fair Value Adjustment Additional available credit with the entity Line of Credit Facility, Remaining Borrowing Capacity Investment Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Option Adjusted Spread Option Adjusted Spread [Member] Option Adjusted Spread Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Margin, liability Derivative Asset, Subject to Master Netting Arrangement, Collateral, Obligation to Return Cash Not Offset Interest expense: Interest Expense, Operating and Nonoperating [Abstract] Derivative liability, subject to master netting arrangement, asset offset Derivative Liability, Subject to Master Netting Arrangement, Asset Offset Purchases Payments to Acquire Debt Securities, Available-for-Sale Preferred stock (par value $0.0001; 20,000,000 authorized; 30,000 shares (12,000,000 depositary shares) issued and outstanding and liquidation value per depositary share of $25 at March 31, 2026 and December 31, 2025) Preferred Stock, Value, Issued Option adjusted spread Schedule of Sensitivity Analysis of Fair Value, Interest Rate Change [Abstract] Schedule of Sensitivity Analysis of Fair Value, Interest Rate Change Year before current fiscal year Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year Derivative Liabilities, Margin Derivative Netting Adjustments, Liabilities Derivative Netting Adjustments, Liabilities Subordinated Debt Subordinated Debt [Member] Financial Asset, Period Past Due [Axis] Financial Asset, Aging [Axis] All Executive Categories All Executive Categories [Member] Loans, including fees Interest and Fee Income, Loans and Leases Gain/(Loss) on Swaps Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments Share-Based Payment Arrangement, Employee Share-Based Payment Arrangement, Employee [Member] Disbursements and escrow fees Disbursements And Escrow Fees [Member] Disbursements And Escrow Fees Commitments and contingencies (Note 15) Commitments and Contingencies Schedule of Held for Investment Loan Portfolio Composition of Loans, Leases and Allowance for Credit Losses Schedule Of Composition Of Loans Held For Investment Portfolio Table [Table Text Block] Schedule of composition of loans held for investment portfolio. Current fiscal year, writeoff Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff Noncontrolling Interest in Subsidiary Noncontrolling Interest [Member] Unrealized holding gains (losses) on SERP Supplemental Employee Retirement Plan [Member] Valuation Allowance [Line Items] Valuation Allowance [Line Items] Interest income Interest Income [Member] Recorded investment for which formal foreclosure proceedings are in process Mortgage Loans in Process of Foreclosure, Amount Cumulative Fair Value Hedging Adjustment Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease) PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Securities available for sale, After ten years, Estimated Fair Value Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Carrying Value of Hedged Liabilities Hedged Liability, Fair Value Hedge Properties acquired through foreclosure Real Estate Acquired Through Foreclosure, Number Of Properties Held Real Estate Acquired Through Foreclosure, Number Of Properties Held Debt Securities, Held-to-maturity, Allowance for Credit Loss [Table] Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Table] 60-89 Days Past Due Financial Asset, 60 to 89 Days Past Due [Member] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Loan servicing fees, net Loan servicing fees, net [Member] Loan servicing fees, net Total liabilities and equity Liabilities And Equity, Excluding Excess Funds Provided (Used) Liabilities And Equity, Excluding Excess Funds Provided (Used) Unrealized loss on SERP, net of tax effect of $0.1 and $—, respectively Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Derivative Contract [Domain] Derivative Contract [Domain] Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] Gross losses Debt Securities, Available-for-Sale, Realized Loss Securities held to maturity, After ten years, Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 10 All Individuals All Individuals [Member] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Residential Residential Real Estate [Member] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Name Forgone Recovery, Individual Name Unrealized gain (loss) on derivatives Unrealized Gain (Loss) on Derivatives Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward] Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Individually Evaluated for Credit Loss Financing Receivable, Individually Evaluated for Credit Loss Weighted average borrowing rate Debt, Weighted Average Interest Rate Four years before current fiscal year, writeoff Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff Debt Securities, Held-to-Maturity [Table] Debt Securities, Held-to-Maturity [Table] Funds transfer pricing Interest Expense, Funds Transfer Pricing Interest Expense, Funds Transfer Pricing Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Net gain on loan origination and sale activities Net gain on loan origination and sale activities [Member] Net gain on loan origination and sale activities Other borrowings Other Borrowings Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Fair value option, aggregate difference Fair Value, Option, Loans Held as Assets, Aggregate Difference Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Title of 12(b) Security Title of 12(b) Security Provision for (Recovery of) Credit Losses Financing Receivable, Excluding Accrued Interest, Credit Loss Expense (Reversal) Cash paid during the period for: Income Taxes Paid, Net [Abstract] Earnings per share: Earnings Per Share [Abstract] Mortgage servicing rights capitalized upon sale of loans MSR capitalized upon sale of loan MSR capitalized upon sale of loan EBO Purchased from Ginnie Mae [Member] Purchased from Ginnie Mae as part of the early buyout program Two years before current fiscal year, writeoff Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] External Credit Rating by Grouping [Axis] External Credit Rating by Grouping [Axis] Credit card guarantees Credit Card Commitments And Financial Guarantees [Member] Credit card commitments and financial guarantees. Interest income related to amortization of cumulative basis adjustment (less than for current period) Interest Income, Hedge Basis Adjustment, Portfolio Layer Method, Increase (Decrease) Ancillary income associated with the Company's MSR portfolio Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset Award Timing Disclosures [Line Items] Income (loss) from equity investments Income (loss) from equity investments [Member] Income (loss) from equity investments Gains and Losses on Sales of Investment Securities Gain (Loss) on Securities [Table Text Block] Measurement Frequency [Domain] Measurement Frequency [Domain] Federal Home Loan Bank Advances Federal Home Loan Bank Advances [Member] Other comprehensive (loss) income before reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Grant year 2024 Grant Year 2024 [Member] Grant Year 2024 Equity Equity [Text Block] Cost to service Cost to Service [Member] Cost to Service Loan Restructuring Modification [Domain] Loan Restructuring Modification [Domain] Other Other, loan segment [Member] Other, loan segment Net losses (gains) on: Gains Losses On [Abstract] (Gains)/Losses on. Net loans HFI Net loans HFI Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss Net income attributable to Western Alliance Net Income (Loss) Attributable to Parent Subsequent Event [Table] Subsequent Event [Table] Redemptions Proceeds From Redemptions Of Equity Securities, FV-NI Proceeds From Redemptions Of Equity Securities, FV-NI CLO Collateralized Loan Obligations [Member] Cash dividends paid on common and preferred stock Payments of Ordinary Dividends, Common Stock And Preferred Stock Payments of Ordinary Dividends, Common Stock And Preferred Stock Vesting period Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Accounts Receivable, Allowance for Credit Loss [Roll Forward] Accounts Receivable, Allowance for Credit Loss [Roll Forward] Reference pool balance Debt Instrument, Reference Pool Balance Debt Instrument, Reference Pool Balance Operating Statistics [Line Items] Segment Reporting Information [Line Items] Preferred stock, shares authorized (shares) Preferred Stock, Shares Authorized Deferred Stock Units Deferred Stock Units [Member] Deferred Stock Units Common stock repurchases Payments for Repurchase of Common Stock Adoption Date Trading Arrangement Adoption Date Reclassifications Reclassification, Comparability Adjustment [Policy Text Block] Futures purchase contracts Futures purchase and sale contracts [Member] Futures purchase and sale contracts Charge-offs Debt Securities, Available-for-Sale, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff Financing Receivable, Past Due [Table] Financing Receivable, Past Due [Table] Other Collateral Other Collateral [Member] Other Collateral [Member] Retained earnings Retained Earnings (Accumulated Deficit) Investment Securities by Credit Rating Type Investment Ratings Position Table [Table Text Block] Investment ratings position. BW Real Estate, Inc. BW Real Estate, Inc. [Member] BW Real Estate, Inc. Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Change in fair value Servicing Asset at Fair Value, Changes in Fair Value Resulting from Changes in Valuation Inputs or Changes in Assumptions Purchases Payments to Acquire Held-to-Maturity Securities Class of Stock [Axis] Class of Stock [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Modified loans on nonaccrual status Financing Receivable, Excluding Accrued Interest, Modified, Nonaccrual Financing Receivable, Excluding Accrued Interest, Modified, Nonaccrual Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Statement [Table] Statement [Table] Valuation Technique, Collateral Method Valuation Technique, Collateral Method [Member] Valuation Technique, Collateral Method Adjustments to reconcile net income to net cash provided by (used in) operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Cash flows from financing activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Risk-free interest rate Measurement Input, Risk Free Interest Rate [Member] Beginning balance (shares) Ending balance (shares) Shares, Issued Securities held to maturity, Mortgage backed securities, Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, without Single Maturity Date All Adjustments to Compensation All Adjustments to Compensation [Member] Grant Year 2023 Grant Year 2023 [Member] Grant Year 2023 Interest Rate Reduction Contractual Interest Rate Reduction [Member] Amendment Flag Amendment Flag Transfers and Servicing [Abstract] Termination Date Trading Arrangement Termination Date Interest bearing deposits in other financial institutions Interest-Bearing Deposits in Banks and Other Financial Institutions Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] 2029 Time Deposit Maturities, Year Three Less: allowance for credit losses Less: allowance for credit losses Total Beginning balance Ending balance Total Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest Junior subordinated debt Junior subordinated debt Subordinated Debt Obligations, Fair Value Disclosure Securities held to maturity, Due in one year or less, Amortized Cost Debt Securities, Held-to-Maturity, Amortized Cost Excluding Accrued Interest, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Year One Loans and Finance Receivables Loans and Finance Receivables [Member] Basic (shares) Weighted average shares - basic (shares) Weighted Average Number of Shares Outstanding, Basic Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Derivative asset, fair value, gross asset including not subject to master netting arrangement Derivative Asset, Gross Asset Including Not Subject to Master Netting Arrangement Deposits by Type Deposit Liabilities, Type [Table Text Block] Subsequent Events [Abstract] Segment Reporting [Abstract] Segment Reporting [Abstract] 10% change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Option Adjusted Spread, 10% Change Sensitivity Analysis of Fair Value, Transferor's Interests in Transferred Financial Assets, Impact of Option Adjusted Spread, 10% Change Amortization of operating lease right of use asset Operating Lease, Expense Prepayable Fixed Rate Loans Prepayable Fixed Rate Loans [Member] Prepayable Fixed Rate Loans Debt [Line Items] Debt Disclosure [Abstract] Share-Based Payment Arrangement, Nonemployee Share-Based Payment Arrangement, Nonemployee [Member] Net gain on AFS securities Net gain on AFS securities Debt Securities, Available-for-Sale, Realized Gain (Loss) Proceeds from sale of other repossessed assets Proceeds from Sale of Foreclosed Assets CRE - owner occupied Commercial Real Estate Owner Occupied [Member] Commercial real estate-owner occupied. Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Common stock, par value (dollars per share) Common Stock, Par or Stated Value Per Share Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Other commercial and industrial Other commercial and industrial [Member] Other commercial and industrial [Member] Loan acquisition and origination fees Loan acquisition and origination fees Loan acquisition and origination fees Deposits, Earnings Credit And Referral Costs Deposits, Earnings Credit And Referral Costs Deposits, Earnings Credit And Referral Costs Other CRE - non-owner occupied Other Commercial Real Estate Non owner Occupied [Member] Other Commercial Real Estate Non owner Occupied [Member] Recoveries Debt Securities, Available-for-Sale, Excluding Accrued Interest, Allowance for Credit Loss, Recovery Use of estimates Use of Estimates, Policy [Policy Text Block] Occupancy Occupancy, Net Fair Value of Assets and Liabilities Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Derivative asset, subject to master netting arrangement, liability offset Derivative Asset, Subject to Master Netting Arrangement, Liability Offset Subsequent Events Subsequent Events [Text Block] Insider Trading Arrangements [Line Items] Five or more years before current fiscal year Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year Available-for-sale debt securities Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost [Abstract] Current Financial Asset, Not Past Due [Member] Investment securities - AFS, ACL Beginning balance Ending balance Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest Total liabilities Total liabilities Liabilities Cash dividends paid to noncontrolling interest Cash dividends paid to noncontrolling interest Payments of Ordinary Dividends, Noncontrolling Interest Interest rate lock commitments Interest Rate Lock Commitments [Member] % of Total Class of Financing Receivable Financing Receivable, Excluding Accrued Interest, Modified in Period, to Total Financing Receivables, Percentage Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Grant year 2022 Grant year 2022 [Member] Grant year 2022 Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Deposit costs Non-Interest Expense Deposit Costs Deposit costs related to non-interest bearing deposits held by the Company for which the Company pays on behalf of customers based on deposit activity during the period Net increase in loans HFI Payments for (Proceeds from) Loans and Leases Savings and money market accounts Deposits, Savings Deposits Value of repossessed properties Other Real Estate, Foreclosed Assets, and Repossessed Assets Other Other Security Investments [Member] Consolidation Items [Axis] Consolidation Items [Axis] Weighted average rate on FHLB advances Federal Home Loan Bank, Advances, Weighted Average Interest Rate Qualifying debt Interest Expense, Subordinated Notes and Debentures Principal pay downs and maturities Proceeds from Maturities, Prepayments and Calls of Held-to-Maturity Securities Investment securities - HTM, at amortized cost and net of ACL of $13.4 and $12.9 (fair value of $1,450 and $1,427) at March 31, 2026 and December 31, 2025, respectively Debt Securities, Held-to-Maturity, Excluding Accrued Interest, after Allowance for Credit Loss Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Collateral posted by this counterparty Collateral Already Posted, Aggregate Fair Value