Nature of Operations and Summary of Significant Accounting Policies	3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations and Summary of Significant Accounting Policies	Note 1 — Nature of Operations and Summary of Significant Accounting Policies Nature of Operations The accounting and reporting practices of First Business Financial Services, Inc. (“FBFS” or the “Corporation”), through our wholly-owned subsidiary, First Business Bank (“FBB” or the “Bank”), have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). FBB operates as a commercial banking institution primarily in Wisconsin and the greater Kansas City metropolitan area. The Bank provides a full range of financial services to businesses, business owners, executives, professionals, and high net worth individuals. FBB also offers bank consulting services to community financial institutions. The Bank is subject to competition from other financial institutions and service providers and is also subject to state and federal regulations. Basis of Presentation The accompanying unaudited Consolidated Financial Statements were prepared in accordance with GAAP and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s Consolidated Financial Statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2025. The unaudited Consolidated Financial Statements include the accounts of the Corporation and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. Management of the Corporation is required to make estimates and assumptions which affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements as well as reported amounts of revenues and expenses during the reporting period. Actual results could differ significantly from those estimates. Material estimates that could significantly change in the near-term include the value of securities and interest rate swaps, level of the allowance for credit losses, lease residuals, property under operating leases, goodwill, and income taxes. The results of operations for the three months ended March 31, 2026 are not necessarily indicative of results that may be expected for any other interim period or the entire fiscal year ending December 31, 2026. Certain amounts in prior periods may have been reclassified to conform to the current presentation. Subsequent events have been evaluated through the date of the issuance of the unaudited Consolidated Financial Statements. No significant subsequent events have occurred through this date requiring adjustment to the financial statements or disclosures. The Corporation has not changed its significant accounting and reporting policies from those disclosed in the Corporation’s Form 10-K for the year ended December 31, 2025. Recent Accounting Pronouncements In November 2024, the FASB issued ASU No. 2024-03, “Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40).” This update improves the transparency and usefulness of financial statements by requiring companies to break down certain expense line items. This update is effective for fiscal years beginning after December 15, 2026. The Corporation will implement this standard when it becomes effective. The adoption of the standard only requires additional disclosures and therefore will not affect net income, stockholders' equity or cash flows. In September 2025, the FASB issued ASU No. 2025-06, “Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software.” This update modernizes the accounting for internal-use software. This update is effective for fiscal years beginning after December 15, 2027. The Corporation is assessing the impact of this standard. In November 2025, the FASB issued ASU No. 2025-09, "Derivatives and Hedging (Subtopic 815): Hedge Accounting Improvements." This update clarifies and improves hedge accounting requirements. This update is effective for fiscal years beginning after December 15, 2026. The Corporation is assessing the impact of this standard.

The accounting and reporting practices of First Business Financial Services, Inc. (“FBFS” or the “Corporation”), through our wholly-owned subsidiary, First Business Bank (“FBB” or the “Bank”), have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). FBB operates as a commercial banking institution primarily in Wisconsin and the greater Kansas City metropolitan area. The Bank provides a full range of financial services to businesses, business owners, executives, professionals, and high net worth individuals. FBB also offers bank consulting services to community financial institutions. The Bank is subject to competition from other financial institutions and service providers and is also subject to state and federal regulations.

The accompanying unaudited Consolidated Financial Statements were prepared in accordance with GAAP and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s Consolidated Financial Statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2025. The unaudited Consolidated Financial Statements include the accounts of the Corporation and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.

Management of the Corporation is required to make estimates and assumptions which affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements as well as reported amounts of revenues and expenses during the reporting period. Actual results could differ significantly from those estimates. Material estimates that could significantly change in the near-term include the value of securities and interest rate swaps, level of the allowance for credit losses, lease residuals, property under operating leases, goodwill, and income taxes. The results of operations for the three months ended March 31, 2026 are not necessarily indicative of results that may be expected for any other interim period or the entire fiscal year ending December 31, 2026. Certain amounts in prior periods may have been reclassified to conform to the current presentation. Subsequent events have been evaluated through the date of the issuance of the unaudited Consolidated Financial Statements. No significant subsequent events have occurred through this date requiring adjustment to the financial statements or disclosures.

The Corporation has not changed its significant accounting and reporting policies from those disclosed in the Corporation’s Form 10-K for the year ended December 31, 2025.

Recent Accounting Pronouncements

In November 2024, the FASB issued ASU No. 2024-03, “Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40).” This update improves the transparency and usefulness of financial statements by requiring companies to break down certain expense line items. This update is effective for fiscal years beginning after December 15, 2026. The Corporation will implement this standard when it becomes effective. The adoption of the standard only requires additional disclosures and therefore will not affect net income, stockholders' equity or cash flows.

In September 2025, the FASB issued ASU No. 2025-06, “Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software.” This update modernizes the accounting for internal-use software. This update is effective for fiscal years beginning after December 15, 2027. The Corporation is assessing the impact of this standard.

In November 2025, the FASB issued ASU No. 2025-09, "Derivatives and Hedging (Subtopic 815): Hedge Accounting Improvements." This update clarifies and improves hedge accounting requirements. This update is effective for fiscal years beginning after December 15, 2026. The Corporation is assessing the impact of this standard.