Summary of Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2026
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. 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 March 31, 2026 and for the three months ended March 31, 2026 and 2025 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, 2025. 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 Purchased Loans In November 2025, the FASB issued guidance within ASU 2025-08, Financial Instruments - Credit Losses (Topic 326): Purchased Loans. The amendments in this update are intended to improve decision usefulness and comparability of financial reporting for acquired financial assets while retaining the measurement, presentation or disclosure requirements outlined in ASC 326. The update introduces the concept of "purchased seasoned loans," which refers to non-purchased credit deteriorated loans acquired in a business combination or in an asset acquisition more than 90 days after their origination date. The amendments align the accounting for purchased seasoned loans with the gross-up methodology applied to purchased credit deteriorated loans, whereby the initial estimate of credit losses is amortized over the life of the loan as a reduction to interest income, rather than being recognized immediately in earnings as credit loss expense. The update also includes an accounting policy election related to the subsequent measurement of expected credit losses on purchased seasoned loans for entities using a method other than a discounted cash flow analysis. Under this election, entities may use the amortized cost basis of the asset, rather than the unpaid principal balance to estimate credit losses on these loans. The amendments in this update are effective for fiscal years beginning after December 15, 2026 and interim periods within those fiscal years. The amendments are to be applied prospectively and early adoption is permitted. The Company is currently evaluating the impact these amendments may have on its Consolidated Financial Statements. 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. Recently adopted accounting guidance Targeted Improvements to the Accounting for Internal-Use Software In September 2025, the FASB issued guidance within ASU 2025-06, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40). The amendments in this update are intended to modernize and improve the accounting for internal-use software costs. The changes aim to make the recognition and capitalization of software costs more consistent across different development methodologies and eliminates the requirement to assess software development costs based on predefined project stages (e.g., preliminary, application development, post-implementation). The update requires entities to start capitalizing software costs when management has authorized and committed to funding the software project and it is probable that the project will be completed and the software will be used to perform the function intended. The Company adopted this guidance on a prospective basis beginning on January 1, 2026. Adoption of this guidance did not have a significant impact on the Company's financial position or results of operations. 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 Company adopted this guidance on a prospective basis beginning with the annual period ending December 31, 2025 and provided these enhanced income tax disclosures in Note 17. Income Taxes of the Notes to Consolidated Financial Statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2025. There was no impact on the Company's financial position or results of operations.
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 March 31, 2026, 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)

3 Months Ended

Mar. 31, 2026

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.

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 March 31, 2026 and for the three months ended March 31, 2026 and 2025 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, 2025. 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

Purchased Loans

In November 2025, the FASB issued guidance within ASU 2025-08, Financial Instruments - Credit Losses (Topic 326): Purchased Loans. The amendments in this update are intended to improve decision usefulness and comparability of financial reporting for acquired financial assets while retaining the measurement, presentation or disclosure requirements outlined in ASC 326. The update introduces the concept of "purchased seasoned loans," which refers to non-purchased credit deteriorated loans acquired in a business combination or in an asset acquisition more than 90 days after their origination date. The amendments align the accounting for purchased seasoned loans with the gross-up methodology applied to purchased credit deteriorated loans, whereby the initial estimate of credit losses is amortized over the life of the loan as a reduction to interest income, rather than being recognized immediately in earnings as credit loss expense. The update also includes an accounting policy election related to the subsequent measurement of expected credit losses on purchased seasoned loans for entities using a method other than a discounted cash flow analysis. Under this election, entities may use the amortized cost basis of the asset, rather than the unpaid principal balance to estimate credit losses on these loans.

The amendments in this update are effective for fiscal years beginning after December 15, 2026 and interim periods within those fiscal years. The amendments are to be applied prospectively and early adoption is permitted. The Company is currently evaluating the impact these amendments may have on its Consolidated Financial Statements.

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.

Recently adopted accounting guidance

Targeted Improvements to the Accounting for Internal-Use Software

In September 2025, the FASB issued guidance within ASU 2025-06, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40). The amendments in this update are intended to modernize and improve the accounting for internal-use software costs. The changes aim to make the recognition and capitalization of software costs more consistent across different development methodologies and eliminates the requirement to assess software development costs based on predefined project stages (e.g., preliminary, application development, post-implementation). The update requires entities to start capitalizing software costs when management has authorized and committed to funding the software project and it is probable that the project will be completed and the software will be used to perform the function intended.

The Company adopted this guidance on a prospective basis beginning on January 1, 2026. Adoption of this guidance did not have a significant impact on the Company's financial position or results of operations.

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 Company adopted this guidance on a prospective basis beginning with the annual period ending December 31, 2025 and provided these enhanced income tax disclosures in Note 17. Income Taxes of the Notes to Consolidated Financial Statements in the Company's Annual Report on Form 10-K for the year ended December 31, 2025. There was no impact on the Company's financial position or results of operations.

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 March 31, 2026, 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.