Regulatory Capital	3 Months Ended
Mar. 31, 2020
Regulatory Capital Requirements [Abstract]
Regulatory Capital	NOTE 14 - REGULATORY CAPITAL The Bank is subject to various regulatory capital requirements administered by the Federal Reserve and the FDIC. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company’s consolidated financial statements. Under capital adequacy guidelines of the regulatory framework for prompt corrective action, the Bank must meet specific capital adequacy guidelines that involve quantitative measures of the Bank’s assets, liabilities, and certain off-balance sheet items as calculated under regulatory accounting practices. The Bank’s capital classification is also subject to qualitative judgments by the regulators about components, risk weightings, and other factors. The federal banking agencies jointly issued a final rule that provides for an optional, simplified measure of capital adequacy, the community bank leverage ratio framework, for qualifying community banking organizations, consistent with Section 201 of the Economic Growth, Regulatory Relief, and Consumer Protection Act. This final rule is applicable to all non-advanced approaches FDIC-supervised institutions with less than $10 billion in total consolidated assets. The community bank leverage ratio (“CBLR”) final rule was effective on January 1, 2020, and will allow qualifying community banking organizations to calculate a leverage ratio to measure capital adequacy. Banks opting into the CBLR framework will not be required to calculate or report risk-based capital. A qualifying community banking organization is defined as having less than $10 billion in total consolidated assets, a leverage ratio greater than 9%, off-balance sheet exposures of 25% or less of total consolidated assets, and trading assets and liabilities of 5% or less of total consolidated assets. The final rule adopts Tier 1 capital and the existing leverage ratio into the community bank leverage ratio framework. A bank electing the framework will not be subject to other capital and leverage requirements. A bank electing the framework that ceases to meet any qualifying criteria in a future period and that has a leverage ratio greater than 8% will be allowed a grace period of two reporting periods to satisfy the CBLR qualifying criteria or comply with the generally applicable capital requirements. A bank may opt out of the framework at any time, without restriction, by reverting to the generally applicable risk-based capital rule. In response to the COVID-19 pandemic, the CARES Act was signed into law on March 27, 2020. Among other things, the CARES Act directs federal banking agencies to adopt interim final rules to lower the threshold under the CBLR from 9% to 8% and to provide a reasonable grace period for a community bank that falls below the threshold to regain compliance, in each case until the earlier of the termination date of the national emergency or December 31, 2020. In April 2020, the federal banking agencies issued two interim final rules implementing this directive. One interim final rule provides that, as of the second quarter 2020, banking organizations with leverage ratios of 8% or greater (and that meet the other existing qualifying criteria) may elect to use the CBLR framework. It also establishes a two-quarter grace period for qualifying community banking organizations whose leverage ratios fall below the 8% CBLR requirement, so long as the banking organization maintains a leverage ratio of 7% or greater. The second interim final rule provides a transition from the temporary 8% CBLR requirement to a 9% CBLR requirement. It establishes a minimum CBLR of 8% for the second through fourth quarters of 2020, 8.5% for 2021, and 9% thereafter, and maintains a two-quarter grace period for qualifying community banking organizations whose leverage ratios fall no more than 100 basis points below the applicable CBLR requirement. The Bank qualified and elected the CBLR framework as of March 31, 2020. The Tier 1 leverage-based capital ratio calculated for the Bank at March 31, 2020 was 11.3%, compared to 11.6% at December 31, 2019. At March 31, 2020, the Bank had Tier 1 capital of $194.3 million and a minimum Tier 1 capital requirement of $138.0 million to be considered well capitalized under the CBLR framework. At December 31, 2019, The Bank had Tier 1 capital of $196.0 million and a minimum Tier 1 capital requirement of $84.8 million to be considered well capitalized for the Tier 1 leverage-based ratio under the Basel Committee on Companying Supervision’s capital guidelines for U.S. Banks (“Basel III”) requirements. At March 31, 2020 and December 31, 2019, the Bank was categorized as well capitalized under applicable regulatory requirements. There are no conditions or events since that notification that management believes have changed the Bank’s category. Management believes, at March 31, 2020, that the Bank met all capital adequacy requirements. FS Bancorp, Inc. is a bank holding company registered with the Federal Reserve. Bank holding companies are subject to capital adequacy requirements of the Federal Reserve under the Bank Holding Company Act of 1956, as amended, and the regulations of the Federal Reserve. Bank holding companies with less than $3.0 billion in assets are generally not subject to compliance with the Federal Reserve’s capital regulations, which are generally the same as the capital regulations applicable to the Bank. The Federal Reserve has a policy that a bank holding company is required to serve as a source of financial and managerial strength to the holding company’s subsidiary bank and expects the holding company’s subsidiary bank to be well capitalized under the prompt corrective action regulations. If FS Bancorp, Inc. was subject to regulatory guidelines for bank holding companies with $3.0 billion or more in assets at March 31, 2020, FS Bancorp, Inc. would have exceeded all regulatory capital requirements. The Tier 1 leverage-based capital ratio calculated for FS Bancorp, Inc. at March 31, 2020 was 11.1%, compared to 11.3% at December 31, 2019.

NOTE 14 - REGULATORY CAPITAL

The Bank is subject to various regulatory capital requirements administered by the Federal Reserve and the FDIC. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company’s consolidated financial statements. Under capital adequacy guidelines of the regulatory framework for prompt corrective action, the Bank must meet specific capital adequacy guidelines that involve quantitative measures of the Bank’s assets, liabilities, and certain off-balance sheet items as calculated under regulatory accounting practices. The Bank’s capital classification is also subject to qualitative judgments by the regulators about components, risk weightings, and other factors.

The federal banking agencies jointly issued a final rule that provides for an optional, simplified measure of capital adequacy, the community bank leverage ratio framework, for qualifying community banking organizations, consistent with Section 201 of the Economic Growth, Regulatory Relief, and Consumer Protection Act. This final rule is applicable to all non-advanced approaches FDIC-supervised institutions with less than $10 billion in total consolidated assets. The community bank leverage ratio (“CBLR”) final rule was effective on January 1, 2020, and will allow qualifying community banking organizations to calculate a leverage ratio to measure capital adequacy. Banks opting into the CBLR framework will not be required to calculate or report risk-based capital. A qualifying community banking organization is defined as having less than $10 billion in total consolidated assets, a leverage ratio greater than 9%, off-balance sheet exposures of 25% or less of total consolidated assets, and trading assets and liabilities of 5% or less of total consolidated assets. The final rule adopts Tier 1 capital and the existing leverage ratio into the community bank leverage ratio framework. A bank electing the framework will not be subject to other capital and leverage requirements. A bank electing the framework that ceases to meet any qualifying criteria in a future period and that has a leverage ratio greater than 8% will be allowed a grace period of two reporting periods to satisfy the CBLR qualifying criteria or comply with the generally applicable capital requirements. A bank may opt out of the framework at any time, without restriction, by reverting to the generally applicable risk-based capital rule.

In response to the COVID-19 pandemic, the CARES Act was signed into law on March 27, 2020. Among other things, the CARES Act directs federal banking agencies to adopt interim final rules to lower the threshold under the CBLR from 9% to 8% and to provide a reasonable grace period for a community bank that falls below the threshold to regain compliance, in each case until the earlier of the termination date of the national emergency or December 31, 2020. In April 2020, the federal banking agencies issued two interim final rules implementing this directive. One interim final rule provides that, as of the second quarter 2020, banking organizations with leverage ratios of 8% or greater (and that meet the other existing qualifying criteria) may elect to use the CBLR framework. It also establishes a two-quarter grace period for qualifying community banking organizations whose leverage ratios fall below the 8% CBLR requirement, so long as the banking organization maintains a leverage ratio of 7% or greater. The second interim final rule provides a transition from the temporary 8% CBLR requirement to a 9% CBLR requirement. It establishes a minimum CBLR of 8% for the second through fourth quarters of 2020, 8.5% for 2021, and 9% thereafter, and maintains a two-quarter grace period for qualifying community banking organizations whose leverage ratios fall no more than 100 basis points below the applicable CBLR requirement.

The Bank qualified and elected the CBLR framework as of March 31, 2020. The Tier 1 leverage-based capital ratio calculated for the Bank at March 31, 2020 was 11.3%, compared to 11.6% at December 31, 2019. At March 31, 2020, the Bank had Tier 1 capital of $194.3 million and a minimum Tier 1 capital requirement of $138.0 million to be considered well capitalized under the CBLR framework. At December 31, 2019, The Bank had Tier 1 capital of $196.0 million and a minimum Tier 1 capital requirement of $84.8 million to be considered well capitalized for the Tier 1 leverage-based ratio under the Basel Committee on Companying Supervision’s capital guidelines for U.S. Banks (“Basel III”) requirements. At March 31, 2020 and December 31, 2019, the Bank was categorized as well capitalized under applicable regulatory requirements. There are no conditions or events since that notification that management believes have changed the Bank’s category. Management believes, at March 31, 2020, that the Bank met all capital adequacy requirements.

FS Bancorp, Inc. is a bank holding company registered with the Federal Reserve. Bank holding companies are subject to capital adequacy requirements of the Federal Reserve under the Bank Holding Company Act of 1956, as amended, and the regulations of the Federal Reserve. Bank holding companies with less than $3.0 billion in assets are generally not subject to compliance with the Federal Reserve’s capital regulations, which are generally the same as the capital regulations applicable to the Bank. The Federal Reserve has a policy that a bank holding company is required to serve as a source of financial and managerial strength to the holding company’s subsidiary bank and expects the holding company’s subsidiary bank to be well capitalized under the prompt corrective action regulations. If FS Bancorp, Inc. was subject to regulatory guidelines for bank holding companies with $3.0 billion or more in assets at March 31, 2020, FS Bancorp, Inc. would have exceeded all regulatory capital requirements. The Tier 1 leverage-based capital ratio calculated for FS Bancorp, Inc. at March 31, 2020 was 11.1%, compared to 11.3% at December 31, 2019.