Regulatory Matters - Requirements (Details) - BankFinancial NA [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Capital [Abstract]
Total capital (to risk-weighted assets), Actual, Amount	$ 170,203	$ 178,664
Total capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	83,130	93,430
Total capital (to risk-weighted assets), Minimum Capital Ratios Established under Capital Plans, Amount	103,913	116,787
Tier One Risk Based Capital [Abstract]
Tier 1 (core) capital (to risk-weighted assets), Actual, Amount	162,455	170,194
Tier 1 (core) capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	62,348	70,072
Tier 1 (core) capital (to risk-weighted assets), Minimum Capital Ratios Established under Capital Plans, Amount	83,130	93,430
Tier One Leverage Capital [Abstract]
Tier 1 (core) capital (to adjusted average total assets), Actual, Amount	162,455	170,194
Tier 1 (core) capital (to adjusted average total assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	59,666	61,721
Tier 1 (core) capital (to adjusted average total assets), Minimum Capital Ratios Established under Capital Plans, Amount	$ 74,583	$ 77,151
Risk Based Ratios [Abstract]
Total capital (to risk-weighted assets), Actual, Ratio	16.38%	15.30%
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio	8.00%	8.00%
Total capital (to risk-weighted assets), Minimum Capital Ratios Established under Capital Plans, Ratio	10.00%	10.00%
Tier 1 (core) capital (to risk-weighted assets), Actual, Ratio	15.63%	14.57%
Tier 1 (core) capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.00%	6.00%
Tier 1 (core) capital (to risk-weighted assets), Minimum Capital Ratios Established under Capital Plans, Ratio	8.00%	8.00%
CET common tier 1 equity	$ 162,455	$ 170,194
Common Tier 1 to Risk Weighted Assets	15.63%	14.57%
Common Tier 1 Risk Based Capital Required for Capital Adequacy	$ 46,761	$ 52,554
Common Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Common Tier One Capital required to be well capitalized	$ 67,543	$ 75,912
Common Tier One Risk Weighted Assets Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Leverage Ratios [Abstract]
Tier 1 (core) capital (to adjusted average total assets), Actual, Ratio	10.89%	11.03%
Tier 1 (core) capital (to adjusted average total assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	4.00%	4.00%
Tier 1 (core) capital (to adjusted average total assets), Minimum Capital Ratios Established under Capital Plans, Ratio	5.00%	5.00%

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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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