Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation	These unaudited interim condensed consolidated financial statements include the accounts of Byline Bancorp, Inc., a Delaware corporation (the “Company,” “Byline,” “we,” “us,” “our”), a bank holding company whose principal activity is the ownership and management of its Illinois state chartered subsidiary bank, Byline Bank (the “Bank”), based in Chicago, Illinois. These unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X as promulgated by the Securities and Exchange Commission (“SEC”). In preparing these financial statements, the Company has evaluated events and transactions subsequent to June 30, 2024 for potential recognition or disclosure. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the financial position and results of operations for the periods presented have been included. Certain information in footnote disclosures normally included in financial statements prepared in accordance with GAAP has been condensed or omitted pursuant to the rules and regulations of the SEC and the accounting standards for interim financial statements. These financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s Consolidated Financial Statements as of December 31, 2023 and 2022 and for each of the three years in the period ended December 31, 2023. The Company has one reportable segment. The Company’s chief operating decision makers evaluate the operations of the Company using consolidated information for purposes of allocating resources and assessing performance. Therefore, segments disclosures are currently not required. In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 855, “Subsequent Events,” the Company’s management has evaluated subsequent events for potential recognition or disclosure through the date of the issuance of these condensed consolidated financial statements. No subsequent events were identified that would have required a change to the condensed consolidated financial statements or disclosure in the notes to the condensed consolidated financial statements.
Accounting Pronouncements Recently Adopted or Issued	The following reflect recent accounting pronouncements that have been adopted or are pending adoption by the Company. Adopted Accounting Pronouncements Fair Value Measurement (Topic 820) - In June 2022, the FASB issued ASU No. 2022-03, Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions. The guidance in the ASU clarifies that a contractual restriction on the sale of an equity security is not considered part of the unit of account on the equity security and, therefore, is not considered in measuring fair value. The ASU also requires additional disclosures about the restriction. The amendments in this update are effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years. The Company evaluated the accounting and disclosure requirements of this update and they did not have a material effect on the consolidated financial statements. Issued Accounting Pronouncements Pending Adoption Business Combinations (Topic 805) - In August 2023, the FASB issued ASU 2023-05, Business Combinations—Joint Venture (JV) Formations: Recognition and Initial Measurement. The guidance requires newly-formed JVs to apply a new basis of accounting to all of its contributed net assets, which results in the JV initially measuring its contributed net assets under ASC 805-20, Business Combinations. The new guidance would be applied prospectively and is effective for all newly-formed joint venture entities with a formation date on or after January 1, 2025, with early adoption permitted. The Company is evaluating the accounting and disclosure requirements of this update and the impact of adopting the new guidance on the consolidated financial statements. Segment Reporting – Improvements to Reportable Segment Disclosures (Topic 280) – In November 2023, the FASB issued ASU 2023-07 to enhance disclosures about significant segment expenses for public entities reporting segment information under Topic 280. It requires that a public entity disclose, on an annual and interim basis, significant expense categories for each reportable segment. Significant expense categories are derived from expenses that are 1) regularly reported to an entity’s chief operating decision-maker ("CODM"), and 2) included in a segment’s reported measure of profit or loss. The disclosures should include an amount for "other segment items," reflecting the difference between 1) segment revenue less significant segment expenses, and 2) the reportable segment’s profit or loss measures. It requires that a public entity disclose the title and position of the CODM and how the CODM uses the reported measure of profit or loss to assess segment performance and to allocate resources. Further it clarifies that entities with a single reportable segment must disclose both new and existing segment reporting requirements. The amendments are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Entities must adopt the guidance on a retrospective basis. The Company is evaluating the internal control and disclosure requirements of this update and the impact of adopting the new guidance on the consolidated financial statements. Income Taxes – Improvements to Income Tax Disclosures (Topic 740) – In December 2023, the FASB issued ASU 2023-09 to provide additional transparency into an entity’s income tax disclosures primarily related to the rate reconciliation and income taxes paid information. The standard requires that public business entities disclose, on an annual basis, specific categories in the rate reconciliation and additional information for reconciling items meeting a certain quantitative threshold. The amendments also require that entities disclose on an annual basis: 1) income taxes paid (net of refunds received) disaggregated by federal (national), state, and foreign taxes and 2) the income taxes paid (net of refunds received) disaggregated by individual jurisdictions exceeding 5% of total income taxes paid (net of refunds received). The amendments are effective for public business entities for annual periods beginning after December 15, 2024. The Company is evaluating the accounting and disclosure requirements of this update and the impact of adopting the new guidance on the consolidated financial statements.

Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2024

These unaudited interim condensed consolidated financial statements include the accounts of Byline Bancorp, Inc., a Delaware corporation (the “Company,” “Byline,” “we,” “us,” “our”), a bank holding company whose principal activity is the ownership and management of its Illinois state chartered subsidiary bank, Byline Bank (the “Bank”), based in Chicago, Illinois.

These unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X as promulgated by the Securities and Exchange Commission (“SEC”). In preparing these financial statements, the Company has evaluated events and transactions subsequent to June 30, 2024 for potential recognition or disclosure. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the financial position and results of operations for the periods presented have been included. Certain information in footnote disclosures normally included in financial statements prepared in accordance with GAAP has been condensed or omitted pursuant to the rules and regulations of the SEC and the accounting standards for interim financial statements. These financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s Consolidated Financial Statements as of December 31, 2023 and 2022 and for each of the three years in the period ended December 31, 2023.

The Company has one reportable segment. The Company’s chief operating decision makers evaluate the operations of the Company using consolidated information for purposes of allocating resources and assessing performance. Therefore, segments disclosures are currently not required.

In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 855, “Subsequent Events,” the Company’s management has evaluated subsequent events for potential recognition or disclosure through the date of the issuance of these condensed consolidated financial statements. No subsequent events were identified that would have required a change to the condensed consolidated financial statements or disclosure in the notes to the condensed consolidated financial statements.

Accounting Pronouncements Recently Adopted or Issued

The following reflect recent accounting pronouncements that have been adopted or are pending adoption by the Company.

Adopted Accounting Pronouncements

Fair Value Measurement (Topic 820) - In June 2022, the FASB issued ASU No. 2022-03, Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions. The guidance in the ASU clarifies that a contractual restriction on the sale of an equity security is not considered part of the unit of account on the equity security and, therefore, is not considered in measuring fair value. The ASU also requires additional disclosures about the restriction. The amendments in this update are effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years. The Company evaluated the accounting and disclosure requirements of this update and they did not have a material effect on the consolidated financial statements.

Issued Accounting Pronouncements Pending Adoption

Business Combinations (Topic 805) - In August 2023, the FASB issued ASU 2023-05, Business Combinations—Joint Venture (JV) Formations: Recognition and Initial Measurement. The guidance requires newly-formed JVs to apply a new basis of accounting to all of its contributed net assets, which results in the JV initially measuring its contributed net assets under ASC 805-20, Business Combinations. The new guidance would be applied prospectively and is effective for all newly-formed joint venture entities with a formation date on or after January 1, 2025, with early adoption permitted. The Company is evaluating the accounting and disclosure requirements of this update and the impact of adopting the new guidance on the consolidated financial statements.

Segment Reporting – Improvements to Reportable Segment Disclosures (Topic 280) – In November 2023, the FASB issued ASU 2023-07 to enhance disclosures about significant segment expenses for public entities reporting segment information under Topic 280. It requires that a public entity disclose, on an annual and interim basis, significant expense categories for each reportable segment. Significant expense categories are derived from expenses that are 1) regularly reported to an entity’s chief operating decision-maker ("CODM"), and 2) included in a segment’s reported measure of profit or loss. The disclosures should include an amount for "other segment items," reflecting the difference between 1) segment revenue less significant segment expenses, and 2) the reportable segment’s profit or loss measures. It requires that a public entity disclose the title and position of the CODM and how the CODM uses the reported measure of profit or loss to assess segment

performance and to allocate resources. Further it clarifies that entities with a single reportable segment must disclose both new and existing segment reporting requirements. The amendments are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Entities must adopt the guidance on a retrospective basis. The Company is evaluating the internal control and disclosure requirements of this update and the impact of adopting the new guidance on the consolidated financial statements.

Income Taxes – Improvements to Income Tax Disclosures (Topic 740) – In December 2023, the FASB issued ASU 2023-09 to provide additional transparency into an entity’s income tax disclosures primarily related to the rate reconciliation and income taxes paid information. The standard requires that public business entities disclose, on an annual basis, specific categories in the rate reconciliation and additional information for reconciling items meeting a certain quantitative threshold. The amendments also require that entities disclose on an annual basis: 1) income taxes paid (net of refunds received) disaggregated by federal (national), state, and foreign taxes and 2) the income taxes paid (net of refunds received) disaggregated by individual jurisdictions exceeding 5% of total income taxes paid (net of refunds received). The amendments are effective for public business entities for annual periods beginning after December 15, 2024. The Company is evaluating the accounting and disclosure requirements of this update and the impact of adopting the new guidance on the consolidated financial statements.