Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	NOTE 1 - BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations - FS Bancorp, Inc. (the “Company”) was incorporated in September 2011 as the holding company for 1st Security Bank of Washington (the “Bank” or “1st Security Bank”) in connection with the Bank’s conversion from the mutual to stock form of ownership which was completed on July 9, 2012. The Bank is a community-based savings bank with 21 full-service bank branches, a headquarters that accepts deposits, and seven home loan production offices in suburban communities in the greater Puget Sound area which includes Snohomish, King, Pierce, Jefferson, Kitsap, Clallam, Grays Harbor, Thurston, and Lewis counties, and one loan production office in the market area of the Tri-Cities, Washington. The Bank provides loan and deposit services to customers who are predominantly small- and middle-market businesses and individuals. The Company and its subsidiary are subject to regulation by certain federal and state agencies and undergo periodic examination by these regulatory agencies. Financial Statement Presentation - The accompanying unaudited interim consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. 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”). It is recommended that these unaudited interim consolidated financial statements be read in conjunction with the Company’s Annual Report on Form 10‑K with all of the audited information and footnotes required by U.S. GAAP for complete financial statements for the year ended December 31, 2019, as filed with the SEC on March 16, 2020. In the opinion of management, all normal adjustments and recurring accruals considered necessary for a fair presentation of the financial position and results of operations for the periods presented have been included. The results for the three months ended March 31, 2020 are not necessarily indicative of the results that may be expected for the year ending December 31, 2020, or any other future period. The preparation of financial statements, in conformity with U.S. GAAP, requires management to make estimates and assumptions that affect amounts reported in the financial statements. Actual results could differ from these estimates. Material estimates that are particularly susceptible to significant change relate to the determination of the allowance for loan and lease losses, fair value of financial instruments, the valuation of servicing rights, deferred income taxes, and if needed, a deferred tax asset valuation allowance. Amounts presented in the consolidated financial statements and footnote tables are rounded and presented to the nearest thousands of dollars except per share amounts. If the amounts are above $1.0 million, they are rounded one decimal point, and if they are above $1.0 billion, they are rounded two decimal points. Principles of Consolidation - The consolidated financial statements include the accounts of FS Bancorp, Inc. and its wholly owned subsidiary, 1st Security Bank of Washington. All material intercompany accounts have been eliminated in consolidation. Segment Reporting - The Company operates in two business segments through the Bank: commercial and consumer banking and home lending. The Company’s business segments are determined based on the products and services provided, as well as the nature of the related business activities, and they reflect the manner in which financial information is regularly reviewed for the purpose of allocating resources and evaluating performance of the Company’s businesses. The results for these business segments are based on management’s accounting process, which assigns income statement items and assets to each responsible operating segment. This process is dynamic and is based on management’s view of the Company’s operations. See “Note 15 - Business Segments.” Subsequent Events - The Company has evaluated events and transactions subsequent to March 31, 2020 for potential recognition or disclosure. RECENT ACCOUNTING PRONOUNCEMENTS In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016‑13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, as amended by ASU 2018-19, ASU 2019-10, and ASU 2019-11. The ASU is intended to improve financial reporting by requiring timelier recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. The ASU requires the recognition and measurement of all current expected credit losses (“CECL”) for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Financial institutions and other organizations will now use forward-looking information to better inform their credit loss estimates. Many of the loss estimation techniques applied today will still be permitted, although the inputs to those techniques will change to reflect the approach under CECL. Organizations will continue to use judgment to determine which loss estimation method is appropriate for their circumstances. The ASU requires enhanced disclosures to help investors and other financial statement users better understand significant estimates and judgments used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. These disclosures include qualitative and quantitative requirements that provide additional information about the amounts recorded in the financial statements. In addition, the ASU amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The ASU and associated amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2022. Early adoption will be permitted for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company has selected a third-party vendor to assist in the implementation of this ASU and has run parallel computations as it continues to evaluate the impact of adoption of the new standard. As part of the implementation, management is also evaluating economic variables and forecast time horizons it believes to be most relevant based on the composition of the loans portfolio to develop a reasonable and supportable forecast, likely to include forecasted levels of employment, gross domestic product, and home price index, depending on the nature of the loan segment, as well as various loss methodologies to estimate expected credit losses. In addition, management has kept current on evolving interpretations and industry practices related to ASU 2016-13 via webcasts, publications, and conferences. Once adopted, the Company anticipates the allowance for loan losses to increase through a one‑time adjustment to retained earnings, however, until the evaluation is complete the magnitude of the potential increase will be unknown. In April 2019, the FASB issued ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments. This ASU clarifies and improves areas of guidance related to the recently issued standards on credit losses, hedging, and recognition and measurement including improvements resulting from various FASB Transition Resource Group meetings. Early adoption is permitted. The Company plans to adopt Topic 326 of this ASU, in conjunction with ASU No. 2016-13, on January 1, 2023. The adoption of Topic 815 is not expected to have a material impact on the Company’s consolidated financial statements. In May 2019, the FASB issued ASU 2019-05, Financial Instruments-Credit Losses (Topic 326): Targeted Transition Relief. The amendments in this ASU provide entities that have certain instruments within the scope of Subtopic 326-20 with an option to irrevocably elect the fair value option in Subtopic 825-10, applied on an instrument-by-instrument basis for eligible instruments, upon the adoption of Topic 326. The fair value option election does not apply to held-to-maturity debt securities. An entity that elects the fair value option should subsequently measure those instruments at fair value with changes in fair value flowing through earnings. This ASU is effective for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. The ASU should be applied on a modified-retrospective basis by means of a cumulative-effect adjustment to the opening balance of retained earnings balance in the balance sheet. Early adoption is permitted. The Company is currently assessing the impact that ASU 2019-05 will have on its consolidated financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740, Income Taxes. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This ASU is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The Company does not expect the adoption of ASU 2019-12 to have a material impact on its consolidated financial statements. In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of reference Rate Reform on Financial Reporting. This ASU applies to contracts, hedging relationships and other transactions that reference LIBOR or other rate references expected to be discontinued because of reference rate reform. The ASU permits an entity to make necessary modifications to eligible contracts or transactions without requiring contract remeasurement or reassessment of a previous accounting determination. For a cash flow hedge, a change in the method used to assess hedge effectiveness will not result in dedesignation of the hedging relationship if certain criteria are met. This ASU is effective for all entities as of March 12, 2020 through December 31, 2022. The Company is party to cash flow hedge arrangements where the hedge effectiveness is based on LIBOR. The Company is currently evaluating the impact of the reference rate reform on the Company’s consolidated financial statements. Recent Events - On March 22, 2020, the federal banking agencies issued an “Interagency Statement on Loan Modifications and Reporting for Financial Institutions Working with Customers Affected by the Coronavirus”. This guidance encourages financial institutions to work prudently with borrowers that may be unable to meet their contractual obligations because of the effects of the novel coronavirus of 2019 (“COVID-19”) pandemic. The guidance provides that short-term modifications (e.g. six months) made on a good faith basis to borrowers who were current as of the implementation date of a relief program are not Troubled Debt Restructurings (“TDRs”). The Coronavirus Aid, Relief, and Economic Security Act of 2020 signed into law on March 27, 2020 ("CARES Act") provided similar guidance around the modification of loans as a result of the COVID-19 pandemic, providing, among other criteria, that modifications made between March 1, 2020, and the earlier of December 31, 2020, or 60 days after the COVID-19 emergency is terminated, on a good faith basis to borrowers who were current as of December 31, 2019, are not TDRs. This includes modifications such as payment deferrals, fee waivers, extensions of repayment terms, or other delays in payment. Borrowers are considered current under the CARES Act if they are not more than 30 days past due on their contractual payments as of December 31, 2019. Through March 31, 2020, the Bank had applied the interagency statement guidance and modified 66 individual loans with aggregate principal balances totaling $12.5 million. More of these types of modifications are likely to be executed in the second quarter of 2020. The majority of these modifications involved short-term extensions and/or interest-only periods. For additional information, see “NOTE 18 - COVID - 19 Pandemic.” Application of New Accounting Guidance Adopted in 2020 On January 1, 2020, the Company adopted FASB ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. This ASU contains some technical adjustments related to the fair value disclosure requirements of public companies. Included in this ASU is the additional disclosure requirement of unrealized gains and losses for the period in recurring level 3 fair value disclosures and the range and weighted average of significant unobservable inputs, among other technical changes. The adoption of ASU 2018-13 did not have a material impact on the Company's consolidated financial statements.

NOTE 1 - BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Nature of Operations - FS Bancorp, Inc. (the “Company”) was incorporated in September 2011 as the holding company for 1st Security Bank of Washington (the “Bank” or “1st Security Bank”) in connection with the Bank’s conversion from the mutual to stock form of ownership which was completed on July 9, 2012. The Bank is a community-based savings bank with 21 full-service bank branches, a headquarters that accepts deposits, and seven home loan production offices in suburban communities in the greater Puget Sound area which includes Snohomish, King, Pierce, Jefferson, Kitsap, Clallam, Grays Harbor, Thurston, and Lewis counties, and one loan production office in the market area of the Tri-Cities, Washington. The Bank provides loan and deposit services to customers who are predominantly small- and middle-market businesses and individuals. The Company and its subsidiary are subject to regulation by certain federal and state agencies and undergo periodic examination by these regulatory agencies.

Financial Statement Presentation - The accompanying unaudited interim consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. 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”). It is recommended that these unaudited interim consolidated financial statements be read in conjunction with the Company’s Annual Report on Form 10‑K with all of the audited information and footnotes required by U.S. GAAP for complete financial statements for the year ended December 31, 2019, as filed with the SEC on March 16, 2020. In the opinion of management, all normal adjustments and recurring accruals considered necessary for a fair presentation of the financial position and results of operations for the periods presented have been included.

The results for the three months ended March 31, 2020 are not necessarily indicative of the results that may be expected for the year ending December 31, 2020, or any other future period. The preparation of financial statements, in conformity with U.S. GAAP, requires management to make estimates and assumptions that affect amounts reported in the financial statements. Actual results could differ from these estimates. Material estimates that are particularly susceptible to significant change relate to the determination of the allowance for loan and lease losses, fair value of financial instruments, the valuation of servicing rights, deferred income taxes, and if needed, a deferred tax asset valuation allowance.

Amounts presented in the consolidated financial statements and footnote tables are rounded and presented to the nearest thousands of dollars except per share amounts. If the amounts are above $1.0 million, they are rounded one decimal point, and if they are above $1.0 billion, they are rounded two decimal points.

Principles of Consolidation - The consolidated financial statements include the accounts of FS Bancorp, Inc. and its wholly owned subsidiary, 1st Security Bank of Washington. All material intercompany accounts have been eliminated in consolidation.

Segment Reporting - The Company operates in two business segments through the Bank: commercial and consumer banking and home lending. The Company’s business segments are determined based on the products and services provided, as well as the nature of the related business activities, and they reflect the manner in which financial information is regularly reviewed for the purpose of allocating resources and evaluating performance of the Company’s businesses. The results for these business segments are based on management’s accounting process, which assigns income statement items and assets to each responsible operating segment. This process is dynamic and is based on management’s view of the Company’s operations. See “Note 15 - Business Segments.”

Subsequent Events - The Company has evaluated events and transactions subsequent to March 31, 2020 for potential recognition or disclosure.

RECENT ACCOUNTING PRONOUNCEMENTS

In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016‑13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, as amended by ASU 2018-19, ASU 2019-10, and ASU 2019-11. The ASU is intended to improve financial reporting by requiring timelier recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. The ASU requires the recognition and measurement of all current expected credit losses (“CECL”) for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Financial institutions and other organizations will now use forward-looking information to better inform their credit loss estimates. Many of the loss estimation techniques applied today will still be permitted, although the inputs to those techniques will change to reflect the approach under CECL. Organizations will continue to use judgment to determine which loss estimation method is appropriate for their circumstances. The ASU requires enhanced disclosures to help investors and other financial statement users better understand significant estimates and judgments used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. These disclosures include qualitative and quantitative requirements that provide additional information about the amounts recorded in the financial statements. In addition, the ASU amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The ASU and associated amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2022. Early adoption will be permitted for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company has selected a third-party vendor to assist in the implementation of this ASU and has run parallel computations as it continues to evaluate the impact of adoption of the new standard. As part of the implementation, management is also evaluating economic variables and forecast time horizons it believes to be most relevant based on the composition of the loans portfolio to develop a reasonable and supportable forecast, likely to include forecasted levels of employment, gross domestic product, and home price index, depending on the nature of the loan segment, as well as various loss methodologies to estimate expected credit losses. In addition, management has kept current on evolving interpretations and industry practices related to ASU 2016-13 via webcasts, publications, and conferences. Once adopted, the Company anticipates the allowance for loan losses to increase through a one‑time adjustment to retained earnings, however, until the evaluation is complete the magnitude of the potential increase will be unknown.

In April 2019, the FASB issued ASU 2019-04, Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments. This ASU clarifies and improves areas of guidance related to the recently issued standards on credit losses, hedging, and recognition and measurement including improvements resulting from various FASB Transition Resource Group meetings. Early adoption is permitted. The Company plans to adopt Topic 326 of this ASU, in conjunction with ASU No. 2016-13, on January 1, 2023. The adoption of Topic 815 is not expected to have a material impact on the Company’s consolidated financial statements.

In May 2019, the FASB issued ASU 2019-05, Financial Instruments-Credit Losses (Topic 326): Targeted Transition Relief. The amendments in this ASU provide entities that have certain instruments within the scope of Subtopic 326-20 with an option to irrevocably elect the fair value option in Subtopic 825-10, applied on an instrument-by-instrument basis for eligible instruments, upon the adoption of Topic 326. The fair value option election does not apply to held-to-maturity debt securities. An entity that elects the fair value option should subsequently measure those instruments at fair value with changes in fair value flowing through earnings. This ASU is effective for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. The ASU should be applied on a modified-retrospective basis by means of a cumulative-effect adjustment to the opening balance of retained earnings balance in the balance sheet. Early adoption is permitted. The Company is currently assessing the impact that ASU 2019-05 will have on its consolidated financial statements.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740, Income Taxes. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This ASU is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The Company does not expect the adoption of ASU 2019-12 to have a material impact on its consolidated financial statements.

In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of reference Rate Reform on Financial Reporting. This ASU applies to contracts, hedging relationships and other transactions that reference LIBOR or other rate references expected to be discontinued because of reference rate reform. The ASU permits an entity to make necessary modifications to eligible contracts or transactions without requiring contract remeasurement or reassessment of a previous accounting determination. For a cash flow hedge, a change in the method used to assess hedge effectiveness will not result in dedesignation of the hedging relationship if certain criteria are met. This ASU is effective for all entities as of March 12, 2020 through December 31, 2022. The Company is party to cash flow hedge arrangements where the hedge effectiveness is based on LIBOR. The Company is currently evaluating the impact of the reference rate reform on the Company’s consolidated financial statements.

Recent Events - On March 22, 2020, the federal banking agencies issued an “Interagency Statement on Loan Modifications and Reporting for Financial Institutions Working with Customers Affected by the Coronavirus”. This guidance encourages financial institutions to work prudently with borrowers that may be unable to meet their contractual obligations because of the effects of the novel coronavirus of 2019 (“COVID-19”) pandemic. The guidance provides that short-term modifications (e.g. six months) made on a good faith basis to borrowers who were current as of the implementation date of a relief program are not Troubled Debt Restructurings (“TDRs”). The Coronavirus Aid, Relief, and Economic Security Act of 2020 signed into law on March 27, 2020 ("CARES Act") provided similar guidance around the modification of loans as a result of the COVID-19 pandemic, providing, among other criteria, that modifications made between March 1, 2020, and the earlier of December 31, 2020, or 60 days after the COVID-19 emergency is terminated, on a good faith basis to borrowers who were current as of December 31, 2019, are not TDRs. This includes modifications such as payment deferrals, fee waivers, extensions of repayment terms, or other delays in payment. Borrowers are considered current under the CARES Act if they are not more than 30 days past due on their contractual payments as of December 31, 2019. Through March 31, 2020, the Bank had applied the interagency statement guidance and modified 66 individual loans with aggregate principal balances totaling $12.5 million. More of these types of modifications are likely to be executed in the second quarter of 2020. The majority of these modifications involved short-term extensions and/or interest-only periods. For additional information, see “NOTE 18 - COVID - 19 Pandemic.”

Application of New Accounting Guidance Adopted in 2020

On January 1, 2020, the Company adopted FASB ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. This ASU contains some technical adjustments related to the fair value disclosure requirements of public companies. Included in this ASU is the additional disclosure requirement of unrealized gains and losses for the period in recurring level 3 fair value disclosures and the range and weighted average of significant unobservable inputs, among other technical changes. The adoption of ASU 2018-13 did not have a material impact on the Company's consolidated financial statements.