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Regulatory Matters - Requirements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Risk Based Ratios [Abstract]
Common Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		4.50%
Consolidated Entities [Member]
Capital [Abstract]
Total capital (to risk-weighted assets), Actual, Amount		$ 195,371
Total capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		91,590
Tier One Risk Based Capital [Abstract]
Tier 1 (core) capital (to risk-weighted assets), Actual, Amount		187,005
Tier 1 (core) capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		68,692
Tier One Leverage Capital [Abstract]
Tier 1 (core) capital (to adjusted average total assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		$ 65,085
Risk Based Ratios [Abstract]
Total capital (to risk-weighted assets), Actual, Ratio		17.06%
Total capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio		8.00%
Tier 1 (core) capital (to risk-weighted assets), Actual, Ratio		16.33%
Tier 1 (core) capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio		6.00%
CET common tier 1 equity		$ 187,005
Common Tier 1 to Risk Weighted Assets		16.33%
Common Tier 1 Risk Based Capital Required for Capital Adequacy		$ 51,519
Leverage Ratios [Abstract]
Tier 1 (core) capital (to adjusted average total assets), Actual, Ratio		11.49%
Tier 1 (core) capital (to adjusted average total assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio		4.00%
BankFinancial NA [Member]
Capital [Abstract]
Total capital (to risk-weighted assets), Actual, Amount	$ 178,664	$ 188,582
Total capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	93,430	91,572
Total capital (to risk-weighted assets), Minimum Capital Ratios Established under Capital Plans, Amount	116,787	114,466
Tier One Risk Based Capital [Abstract]
Tier 1 (core) capital (to risk-weighted assets), Actual, Amount	170,194	180,216
Tier 1 (core) capital (to risk-weighted assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	70,072	68,679
Tier 1 (core) capital (to risk-weighted assets), Minimum Capital Ratios Established under Capital Plans, Amount	93,430	91,572
Tier One Leverage Capital [Abstract]
Tier 1 (core) capital (to adjusted average total assets), Actual, Amount	170,194	180,216
Tier 1 (core) capital (to adjusted average total assets), Minimum required To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	61,721	65,045
Tier 1 (core) capital (to adjusted average total assets), Minimum Capital Ratios Established under Capital Plans, Amount	$ 77,151	$ 81,307
Risk Based Ratios [Abstract]
Total capital (to risk-weighted assets), Actual, Ratio	15.30%	16.48%
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	14.57%	15.74%
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	$ 170,194	$ 180,216
Common Tier 1 to Risk Weighted Assets	14.57%	15.74%
Common Tier 1 Risk Based Capital Required for Capital Adequacy	$ 52,554	$ 51,509
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	$ 75,912	$ 74,403
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	11.03%	11.08%
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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