Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2022
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, 2022 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 for the years ended December 31, 2021, 2020, and 2019. The Company has one reportable segment. The Company’s chief operating decision maker evaluates the operations of the Company using consolidated information for purposes of allocating resources and assessing performance. Therefore, segments disclosures are 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. Certain prior period amounts have been reclassified to conform to current period presentation. These reclassifications did not result in any changes to previously reported net income or stockholders’ equity.
Accounting Pronouncements Recently Adopted or Issued	The following reflect recent accounting pronouncements that have been adopted or are pending adoption by the Company. As the Company qualifies as an emerging growth company and has elected the extended transition period for complying with new or revised accounting pronouncements, it is not subject to new or revised accounting standards applicable to public companies during the extended transition period. The accounting pronouncements pending adoption below reflect effective dates for the Company as an emerging growth company with the extended transition period. Adopted Accounting Pronouncement Income Taxes (Topic 740)—On January 1, 2022, the Company adopted ASU No. 2019-12, Simplifying the Accounting for Income Taxes. The ASU simplifies the accounting for income taxes by removing the following: the exception to the incremental approach for intraperiod tax allocation when there is a loss from continuing operations and income or a gain from other items; the exception to the requirement to or not to recognize a deferred tax liability for a foreign entity when it becomes an equity method investment or it becomes a subsidiary, respectively; and the exception to the general methodology for calculating income taxes in an interim period when a year-to-date loss exceeds the anticipated loss for the year. The amendments in the ASU change current authoritative guidance by requiring the recognition of franchise tax that is partially based on income as an income-based tax and account for any incremental amount incurred as a non-income-based tax; requiring an evaluation when a step up in the tax basis of goodwill should be considered part the of business combination; specifying that it is not required to allocate the consolidated amount of current and deferred tax expense to a legal entity that is not subject to tax in its separate financial statements; and requiring that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. Adoption of the provisions of ASU No. 2019-12 did not impact our financial result for the three or six months ended June 30, 2022. Issued Accounting Pronouncements Pending Adoption Financial Instruments—Credit Losses (Topic 326)—In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2016‑13, Measurement of Credit Losses on Financial Instruments. Current GAAP requires an “incurred loss” methodology for recognizing credit losses that delays recognition until it is probable a loss has been incurred. The main objective of this ASU is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The amendments in this ASU replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The amendments in this ASU require a financial asset (or group of financial assets) measured at amortized cost basis to be presented at the net amount expected to be collected. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial asset(s) to present the net carrying value at the amount expected to be collected on the financial asset. The measurement of expected credit losses will be based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. Upon adoption, a banking organization must record a one-time adjustment to its credit loss allowances as of the beginning of the fiscal year of adoption equal to the difference, if any, between the amount of credit loss allowances under the prior methodology and the amount required under the new standard. The amendments in this ASU broaden the information that an entity must consider in developing its expected credit loss estimate for assets measured either collectively or individually. The use of forecasted information incorporates more timely information in the estimate of expected credit loss, which will be more useful to users of the financial statements. In February 2022, FASB issued ASU No. 2022-02, Troubled Debt Restructurings (TDRs) and Vintage Disclosures, which eliminates the specific accounting guidance for TDRs and updates the vintage disclosure requirements to require disclosure of current period charge-offs by year of origination. This guidance will be implemented upon adoption. In November 2019, FASB issued ASU No. 2019-10, Effective Dates, which delays the effective date of the ASU for entities not classified as Public Business Entities. The Company will adopt the standard on December 31, 2022. The new guidance may result in an increase in the allowance for loan losses, which will reflect the requirement to include expected losses on purchased credit-impaired loans. The extent of the increase will depend on the composition of the loan portfolio, as well as the economic conditions and forecasts as of the adoption date. Reference Rate Reform (Topic 848)—In March 2020, FASB issued ASU No. 2020-04, Facilitation of the Effects of Reference Rate Reform on Financial Reporting. The amendments in the ASU provide optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in the ASU provide optional expedients and exceptions for applying generally accepted accounting principles to contract modifications and hedging relationships, subject to meeting certain criteria, that reference the London Interbank Offered Rate ("LIBOR") or another reference rate expected to be discontinued. The ASU is intended to help stakeholders during the global market-wide reference rate transition period. The amendments in the ASU will be in effect for all entities as of March 12, 2020 through December 31, 2022. Banking regulators have provided guidance which prohibits new financial contracts from referencing LIBOR as the relevant index after December 31, 2021. The guidance goes on to indicate that beginning after June 2023, LIBOR can no longer be used for existing financial contracts. In December 2021, management approved the use of Term Secured Overnight Financing Rate ("SOFR") as an alternative reference rate to LIBOR. Other alternative reference rates may be considered in the future. At June 30, 2022, $1.0 billion of loans, derivatives with a notional amount of $466.9 million, and securities available for sale with a fair value of $47.7 million, include fallback provisions that define the trigger events (an occurrence that precipitates the conversion from LIBOR to a new reference rate), and allow for the selection of a benchmark replacement and a spread adjustment between LIBOR and that benchmark replacement. Junior subordinated debentures carrying value of $37.1 million were also tied to LIBOR.

Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2022

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, 2022 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 for the years ended December 31, 2021, 2020, and 2019.

The Company has one reportable segment. The Company’s chief operating decision maker evaluates the operations of the Company using consolidated information for purposes of allocating resources and assessing performance. Therefore, segments disclosures are 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.

Certain prior period amounts have been reclassified to conform to current period presentation. These reclassifications did not result in any changes to previously reported net income or stockholders’ equity.

Accounting Pronouncements Recently Adopted or Issued

The following reflect recent accounting pronouncements that have been adopted or are pending adoption by the Company. As the Company qualifies as an emerging growth company and has elected the extended transition period for complying with new or revised accounting pronouncements, it is not subject to new or revised accounting standards applicable to public companies during the extended transition period. The accounting pronouncements pending adoption below reflect effective dates for the Company as an emerging growth company with the extended transition period.

Adopted Accounting Pronouncement

Income Taxes (Topic 740)—On January 1, 2022, the Company adopted ASU No. 2019-12, Simplifying the Accounting for Income Taxes. The ASU simplifies the accounting for income taxes by removing the following: the exception to the incremental approach for intraperiod tax allocation when there is a loss from continuing operations and income or a gain from other items; the exception to the requirement to or not to recognize a deferred tax liability for a foreign entity when it becomes an equity method investment or it becomes a subsidiary, respectively; and the exception to the general methodology for calculating income taxes in an interim period when a year-to-date loss exceeds the anticipated loss for the year. The amendments in the ASU change current authoritative guidance by requiring the recognition of franchise tax that is partially based on income as an income-based tax and account for any incremental amount incurred as a non-income-based tax; requiring an evaluation when a step up in the tax basis of goodwill should be considered part the of business combination; specifying that it is not required to allocate the consolidated amount of current and deferred tax expense to a legal entity that is not subject to tax in its separate financial statements; and requiring that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. Adoption of the provisions of ASU No. 2019-12 did not impact our financial result for the three or six months ended June 30, 2022.

Issued Accounting Pronouncements Pending Adoption

Financial Instruments—Credit Losses (Topic 326)—In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2016‑13, Measurement of Credit Losses on Financial Instruments. Current GAAP requires an “incurred loss” methodology for recognizing credit losses that delays recognition until it is probable a loss has been incurred. The main objective of this ASU is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The amendments in this ASU replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The amendments in this ASU require a financial asset (or group of financial assets) measured at amortized cost basis to be presented at the net amount expected to be collected. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial asset(s) to present the net carrying value at the amount expected to be collected on the financial asset. The measurement of expected credit losses will be based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. Upon adoption, a banking organization must record a one-time adjustment to its credit loss allowances as of the beginning of the fiscal year of adoption equal to the difference, if any, between the amount of credit loss allowances under the prior methodology and the amount required under the new standard. The amendments in this ASU broaden the information that an entity must consider in developing its expected credit loss estimate for assets measured either collectively or individually. The use of forecasted information incorporates more timely information in the estimate of expected credit loss, which will be more useful to users of the financial statements. In February 2022, FASB issued ASU No. 2022-02, Troubled Debt Restructurings (TDRs) and Vintage Disclosures, which eliminates the specific accounting guidance for TDRs and updates the vintage disclosure requirements to require disclosure of current period charge-offs by year of origination. This guidance will be implemented upon adoption. In November 2019, FASB issued ASU No. 2019-10, Effective Dates, which delays the effective date of the ASU for entities not classified as Public Business Entities. The Company will adopt the standard on December 31, 2022. The new guidance may result in an increase in the allowance for loan losses, which will reflect the requirement to include expected losses on purchased credit-impaired loans. The extent of the increase will depend on the composition of the loan portfolio, as well as the economic conditions and forecasts as of the adoption date.

Reference Rate Reform (Topic 848)—In March 2020, FASB issued ASU No. 2020-04, Facilitation of the Effects of Reference Rate Reform on Financial Reporting. The amendments in the ASU provide optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in the ASU provide optional expedients and exceptions for applying generally accepted accounting principles to contract modifications and hedging relationships, subject to meeting certain criteria, that reference the London Interbank Offered Rate ("LIBOR") or another reference rate expected to be discontinued. The ASU is intended to help stakeholders during the global market-wide reference rate transition period. The amendments in the ASU will be in effect for all entities as of March 12, 2020 through December 31, 2022. Banking regulators have provided guidance which prohibits new financial contracts from referencing LIBOR as the relevant index after December 31, 2021. The guidance goes on to indicate that beginning after June 2023, LIBOR can no longer be used for existing financial contracts. In December 2021, management approved the use of Term Secured Overnight Financing Rate ("SOFR") as an alternative reference rate to LIBOR. Other alternative reference rates may be considered in the future. At June 30, 2022, $1.0 billion of loans, derivatives with a notional amount of $466.9 million, and securities available for sale with a fair value of $47.7 million, include fallback provisions that define the trigger events (an occurrence that precipitates the conversion from LIBOR to a new reference rate), and allow for the selection of a benchmark replacement and a spread adjustment between LIBOR and that benchmark replacement. Junior subordinated debentures carrying value of $37.1 million were also tied to LIBOR.