Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2025
Accounting Policies [Abstract]
Nature of operations	Nature of operations WAL is a bank holding company headquartered in Phoenix, Arizona, incorporated under the laws of the state of Delaware. WAL provides a full spectrum of customized loan, deposit, and treasury management capabilities, including funds transfer and other digital payment offerings through its wholly-owned banking subsidiary, WAB, together with its banking divisions: ABA, BON, FIB, Bridge, and TPB. The Company also serves business customers through a national platform of specialized financial services, including mortgage banking services through AmeriHome and digital payment services for the class action legal industry. In addition, the Company has the following non-bank subsidiaries: CSI, a captive insurance company formed and licensed under the laws of the state of Arizona and established as part of the Company's overall enterprise risk management strategy, and WATC, which provides corporate trust services and levered loan administration solutions.
Basis of presentation	Basis of presentation The accompanying Unaudited Consolidated Financial Statements as of June 30, 2025 and for the three and six months ended June 30, 2025 and 2024 have been prepared in accordance with GAAP for interim financial information and Article 10 of Regulation S-X and, therefore, do not include all of the information and footnotes required by GAAP for complete financial statements. Accordingly, these statements should be read in conjunction with the Company's audited Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2024. The accounts of the Company and its consolidated subsidiaries are included in the Consolidated Financial Statements. The information furnished in these interim statements reflects all adjustments that are, in the opinion of management, necessary for a fair statement of the results for each respective period presented. Such adjustments are of a normal, recurring nature. The results of operations in the interim statements are not necessarily indicative of the results that may be expected for any other quarter or for the full year.
Recent accounting pronouncements and Recently adopted accounting guidance	Recent accounting pronouncements Disaggregation of Income Statement Expenses In November 2024, the FASB issued guidance within ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Topic 220). The amendments in this update require disclosure, in the notes to financial statements, of specified information about certain costs and expenses. Entities will be required to disclose the amounts of employee compensation, depreciation, and intangible asset amortization included in each relevant expense caption. The update also requires entities to include certain amounts that are already required to be disclosed under current GAAP in the same disclosure as the other disaggregation requirements, disclose a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively, and disclose the total amount of selling expenses and, in annual reporting periods, an entity’s definition of selling expenses. The amendments in this update are effective for fiscal years beginning after December 15, 2026 and interim periods within fiscal years beginning after December 15, 2027 and may be applied on a prospective or retrospective basis. The Company is currently evaluating the impact these amendments will have on its Consolidated Financial Statements. Improvements to Income Tax Disclosures In December 2023, the FASB issued guidance within ASU 2023-09, Income Taxes (Topic 740). The amendments in this update are intended to increase visibility into various income tax components that affect the reconciliation of the effective tax rate to the statutory rate, as well as the qualitative and quantitative aspects of those components. Public business entities will be required to disclose on an annual basis, specific categories in the rate reconciliation and provide additional information for reconciling items that meet or exceed a five percent threshold (computed by multiplying pretax income by the applicable statutory income tax rate) and include disclosure of state and local jurisdictions that make up the majority of the state and local income tax category in the rate reconciliation. Additional disclosure items include disaggregation of income taxes paid to and income tax expense from federal, state, and foreign jurisdictions as well as disaggregation of income taxes paid to individual jurisdictions in which income taxes paid are equal to or greater than five percent of total income taxes paid. The amendments in this update are effective for fiscal years beginning after December 15, 2024 and interim periods within fiscal years beginning after December 15, 2025 and may be applied on a prospective or retrospective basis. As the amendments in this update relate entirely to enhanced disclosure requirements, adoption of this guidance will not have an impact on the Company's financial position or results of operations. Upon adoption, the Company expects to provide these enhanced income tax disclosures. Recently adopted accounting guidance Improvements to Reportable Segment Disclosures In November 2023, the FASB issued guidance within ASU 2023-07, Segment Reporting (Topic 280). The amendments in this update are intended to improve reportable segment disclosure requirements, primarily through enhanced disclosures related to significant segment expenses. The amendments did not change how an entity identifies its operating segments, aggregates those operating segments, or applies the quantitative thresholds to determine its reportable segments, and all existing segment disclosure requirements in ASC 280 and other Codification topics remain unchanged. The amendments in this update are incremental and require public entities that report segment information to disclose, on an annual and interim basis, significant segment expenses that are regularly provided to the chief operating decision maker and included within each reported measure of segment profit or loss as well as other segment items. Annual disclosure of the title and position of the chief operating decision maker and how the reported measures of segment profit or loss are used to assess performance and allocation of resources is also required. The Company adopted this guidance beginning with the annual period ending December 31, 2024 and applied these updates on a retrospective basis. Upon adoption, the Company provided additional expense detail within its segment disclosures and there was no impact on the Company's financial position or results of operations. Accounting for and Disclosure of Crypto Assets In December 2023, the FASB issued guidance within ASU 2023-08, Intangibles — Goodwill and Other — Crypto Assets (Topic 350). The amendments in this update require entities that hold certain crypto assets to measure such assets at fair value and recognize any changes in fair value in net income in each reporting period. Entities will also be required to present crypto assets measured at fair value separately from other intangible assets on the balance sheet and changes from the remeasurement of crypto assets separately from changes in the carrying amounts of other intangible assets in the income statement. Other disclosure items include the name, cost basis, fair value, and number of units for each significant crypto asset holding and the aggregate fair values and cost bases of crypto asset holdings that are not individually significant along with a rollforward of activity in the reporting period and disclosure of the method for determining the cost basis of the crypto assets. The Company adopted this accounting guidance on January 1, 2025. Although the Company has digital payment offerings, it does not currently hold crypto assets meeting the criteria outlined in the update. Accordingly, the adoption of this guidance did not have an impact on the Company's Consolidated Financial Statements.
Use of estimates	Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management's estimates and judgments are ongoing and are based on experience, current and expected future conditions, third-party evaluations and various other assumptions that management believes are reasonable under the circumstances. The results of these estimates form the basis for making judgments about the carrying values of assets and liabilities, as well as identifying and assessing the accounting treatment with respect to commitments and contingencies. Actual results may differ from those estimates and assumptions used in the Consolidated Financial Statements and related notes. Material estimates susceptible to significant changes in the near term, relate to: 1) the determination of the ACL; 2) certain assets and liabilities carried at fair value; and 3) accounting for income taxes.
Principles of consolidation	Principles of consolidation As of June 30, 2025, WAL has the following significant wholly-owned subsidiaries: WAB and eight unconsolidated subsidiaries used as business trusts in connection with the issuance of trust-preferred securities. WAB has the following significant subsidiaries: 1) WABT, which holds certain investment securities, municipal and nonprofit loans, and leases; 2) WA PWI, which holds interests in certain limited partnerships invested primarily in low income housing tax credits and small business investment corporations; 3) Helios Prime, which holds interests in certain limited partnerships invested in renewable energy projects; 4) BW, which operates as a real estate investment trust and holds certain of WAB's real estate loans and related securities; and 5) Western Finance Company, which purchases and originates equipment finance leases and provides mortgage banking services through its wholly-owned subsidiary, AmeriHome. The Company does not have any other significant entities that should be consolidated. All significant intercompany balances and transactions have been eliminated in consolidation.
Reclassifications	Reclassifications Certain amounts in the Consolidated Income Statements for the prior periods have been reclassified to conform to the current presentation. The reclassifications had no effect on net income or stockholders’ equity as previously reported.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2025

WAL is a bank holding company headquartered in Phoenix, Arizona, incorporated under the laws of the state of Delaware. WAL provides a full spectrum of customized loan, deposit, and treasury management capabilities, including funds transfer and other digital payment offerings through its wholly-owned banking subsidiary, WAB, together with its banking divisions: ABA, BON, FIB, Bridge, and TPB.

The Company also serves business customers through a national platform of specialized financial services, including mortgage banking services through AmeriHome and digital payment services for the class action legal industry. In addition, the Company has the following non-bank subsidiaries: CSI, a captive insurance company formed and licensed under the laws of the state of Arizona and established as part of the Company's overall enterprise risk management strategy, and WATC, which provides corporate trust services and levered loan administration solutions.

Basis of presentation

The accompanying Unaudited Consolidated Financial Statements as of June 30, 2025 and for the three and six months ended June 30, 2025 and 2024 have been prepared in accordance with GAAP for interim financial information and Article 10 of Regulation S-X and, therefore, do not include all of the information and footnotes required by GAAP for complete financial statements. Accordingly, these statements should be read in conjunction with the Company's audited Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2024. The accounts of the Company and its consolidated subsidiaries are included in the Consolidated Financial Statements.

The information furnished in these interim statements reflects all adjustments that are, in the opinion of management, necessary for a fair statement of the results for each respective period presented. Such adjustments are of a normal, recurring nature. The results of operations in the interim statements are not necessarily indicative of the results that may be expected for any other quarter or for the full year.

Recent accounting pronouncements and Recently adopted accounting guidance

Recent accounting pronouncements

Disaggregation of Income Statement Expenses

In November 2024, the FASB issued guidance within ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Topic 220). The amendments in this update require disclosure, in the notes to financial statements, of specified information about certain costs and expenses. Entities will be required to disclose the amounts of employee compensation, depreciation, and intangible asset amortization included in each relevant expense caption. The update also requires entities to include certain amounts that are already required to be disclosed under current GAAP in the same disclosure as the other disaggregation requirements, disclose a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively, and disclose the total amount of selling expenses and, in annual reporting periods, an entity’s definition of selling expenses.

The amendments in this update are effective for fiscal years beginning after December 15, 2026 and interim periods within fiscal years beginning after December 15, 2027 and may be applied on a prospective or retrospective basis. The Company is currently evaluating the impact these amendments will have on its Consolidated Financial Statements.

Improvements to Income Tax Disclosures

In December 2023, the FASB issued guidance within ASU 2023-09, Income Taxes (Topic 740). The amendments in this update are intended to increase visibility into various income tax components that affect the reconciliation of the effective tax rate to the statutory rate, as well as the qualitative and quantitative aspects of those components. Public business entities will be required to disclose on an annual basis, specific categories in the rate reconciliation and provide additional information for reconciling items that meet or exceed a five percent threshold (computed by multiplying pretax income by the applicable statutory income tax rate) and include disclosure of state and local jurisdictions that make up the majority of the state and local income tax category in the rate reconciliation. Additional disclosure items include disaggregation of income taxes paid to and income tax expense from federal, state, and foreign jurisdictions as well as disaggregation of income taxes paid to individual jurisdictions in which income taxes paid are equal to or greater than five percent of total income taxes paid.

The amendments in this update are effective for fiscal years beginning after December 15, 2024 and interim periods within fiscal years beginning after December 15, 2025 and may be applied on a prospective or retrospective basis. As the amendments in this update relate entirely to enhanced disclosure requirements, adoption of this guidance will not have an impact on the Company's financial position or results of operations. Upon adoption, the Company expects to provide these enhanced income tax disclosures.

Recently adopted accounting guidance

Improvements to Reportable Segment Disclosures

In November 2023, the FASB issued guidance within ASU 2023-07, Segment Reporting (Topic 280). The amendments in this update are intended to improve reportable segment disclosure requirements, primarily through enhanced disclosures related to significant segment expenses. The amendments did not change how an entity identifies its operating segments, aggregates those operating segments, or applies the quantitative thresholds to determine its reportable segments, and all existing segment disclosure requirements in ASC 280 and other Codification topics remain unchanged. The amendments in this update are incremental and require public entities that report segment information to disclose, on an annual and interim basis, significant segment expenses that are regularly provided to the chief operating decision maker and included within each reported measure of segment profit or loss as well as other segment items. Annual disclosure of the title and position of the chief operating decision maker and how the reported measures of segment profit or loss are used to assess performance and allocation of resources is also required.

The Company adopted this guidance beginning with the annual period ending December 31, 2024 and applied these updates on a retrospective basis. Upon adoption, the Company provided additional expense detail within its segment disclosures and there was no impact on the Company's financial position or results of operations.

Accounting for and Disclosure of Crypto Assets

In December 2023, the FASB issued guidance within ASU 2023-08, Intangibles — Goodwill and Other — Crypto Assets (Topic 350). The amendments in this update require entities that hold certain crypto assets to measure such assets at fair value and recognize any changes in fair value in net income in each reporting period. Entities will also be required to present crypto assets measured at fair value separately from other intangible assets on the balance sheet and changes from the remeasurement of crypto assets separately from changes in the carrying amounts of other intangible assets in the income statement. Other disclosure items include the name, cost basis, fair value, and number of units for each significant crypto asset holding and the aggregate fair values and cost bases of crypto asset holdings that are not individually significant along with a rollforward of activity in the reporting period and disclosure of the method for determining the cost basis of the crypto assets.

The Company adopted this accounting guidance on January 1, 2025. Although the Company has digital payment offerings, it does not currently hold crypto assets meeting the criteria outlined in the update. Accordingly, the adoption of this guidance did not have an impact on the Company's Consolidated Financial Statements.

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management's estimates and judgments are ongoing and are based on experience, current and expected future conditions, third-party evaluations and various other assumptions that management believes are reasonable under the circumstances. The results of these estimates form the basis for making judgments about the carrying values of assets and liabilities, as well as identifying and assessing the accounting treatment with respect to commitments and contingencies. Actual results may differ from those estimates and assumptions used in the Consolidated Financial Statements and related notes. Material estimates susceptible to significant changes in the near term, relate to: 1) the determination of the ACL; 2) certain assets and liabilities carried at fair value; and 3) accounting for income taxes.

Principles of consolidation

As of June 30, 2025, WAL has the following significant wholly-owned subsidiaries: WAB and eight unconsolidated subsidiaries used as business trusts in connection with the issuance of trust-preferred securities.

WAB has the following significant subsidiaries: 1) WABT, which holds certain investment securities, municipal and nonprofit loans, and leases; 2) WA PWI, which holds interests in certain limited partnerships invested primarily in low income housing tax credits and small business investment corporations; 3) Helios Prime, which holds interests in certain limited partnerships invested in renewable energy projects; 4) BW, which operates as a real estate investment trust and holds certain of WAB's real estate loans and related securities; and 5) Western Finance Company, which purchases and originates equipment finance leases and provides mortgage banking services through its wholly-owned subsidiary, AmeriHome.

The Company does not have any other significant entities that should be consolidated. All significant intercompany balances and transactions have been eliminated in consolidation.

Reclassifications

Certain amounts in the Consolidated Income Statements for the prior periods have been reclassified to conform to the current presentation. The reclassifications had no effect on net income or stockholders’ equity as previously reported.