Regulatory Capital (Details) $ in Thousands	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Actual and Required Capital Amounts and Ratios [Abstract]
Total capital (to risk-weighted assets)	$ 402,690	$ 404,748
Tier I capital (to risk-weighted assets)		392,361
Common Equity Tier 1 Capital (to risk-weighted assets)	384,956	392,361
Tier I capital (to average assets)	$ 384,956	$ 392,361
Total capital (to risk-weighted assets) Ratio	0.2364	0.2617
Tier I capital (to risk-weighted assets) Ratio		0.2537
Common Equity Tier 1 capital (to risk-weighted assets) Ratio	0.2260	0.2537
Tier I capital (to average assets) Ratio	0.1780	0.1969
Total capital (to risk-weighted assets), For Capital Adequacy Purposes	$ 136,268	$ 123,731
Tier I capital (to risk-weighted assets), For Capital Adequacy Purposes		92,799
Common Equity Tier I capital (to risk weighted assets), For Capital Adequacy Purposes	76,651	69,599
Tier I capital (to average assets), For Capital Adequacy Purposes	$ 86,495	$ 79,691
Total capital (to risk-weighted assets), For Capital Adequacy Ratio	0.0800	0.0800
Tier I capital (to risk-weighted assets), For Capital Adequacy Ratio		0.0600
Common Equity Tier I capital (to risk-weighted), For Capital Adequacy Ratio	0.0450	0.0450
Tier I capital (to average assets), For Capital Adequacy Ratio	0.0400	0.0400
Total capital (to risk-weighted assets), Minimum Capital Adequacy with Capital Buffer	$ 178,851	$ 162,398
Tier I capital (to risk weighted assets), Minimum Capital Adequacy with Capital Buffer		131,465
Common Equity Tier I capital (to risk weighted assets) Minimum Capital Adequacy with Capital Buffer	$ 119,234	$ 108,265
Total capital (to risk-weighted assets), Minimum Capital Adequacy with Capital Buffer Ratio	10.50%	10.50%
Tier I capital (to risk weighted assets), Minimum Capital Adequacy with Capital Buffer Ratio		8.50%
Common Equity Tier I capital (to risk weighted), Minimum Capital Adequacy with Capital Buffer Ratio	7.00%	7.00%
Waterstone Bank [Member]
Actual and Required Capital Amounts and Ratios [Abstract]
Total capital (to risk-weighted assets)	$ 386,104	$ 353,357
Tier I capital (to risk-weighted assets)	368,370	340,970
Common Equity Tier 1 Capital (to risk-weighted assets)	368,370	340,970
Tier I capital (to average assets)	368,370	340,970
State of Wisconsin (to total assets)	$ 368,370	$ 340,970
Total capital (to risk-weighted assets) Ratio	0.2268	0.2285
Tier I capital (to risk-weighted assets) Ratio	0.2164	0.2205
Common Equity Tier 1 capital (to risk-weighted assets) Ratio	0.2164	0.2205
Tier I capital (to average assets) Ratio	0.1704	0.1711
State of Wisconsin (to total assets) Ratio	16.62%	17.11%
Total capital (to risk-weighted assets), For Capital Adequacy Purposes	$ 136,165	$ 123,716
Tier I capital (to risk-weighted assets), For Capital Adequacy Purposes	102,124	92,787
Common Equity Tier I capital (to risk weighted assets), For Capital Adequacy Purposes	76,593	69,590
Tier I capital (to average assets), For Capital Adequacy Purposes	86,495	79,691
State of Wisconsin (to total assets), For Capital Adequacy Purposes	$ 133,021	$ 119,590
Total capital (to risk-weighted assets), For Capital Adequacy Ratio	0.0800	0.0800
Tier I capital (to risk-weighted assets), For Capital Adequacy Ratio	0.0600	0.0600
Common Equity Tier I capital (to risk-weighted), For Capital Adequacy Ratio	0.0450	0.0450
Tier I capital (to average assets), For Capital Adequacy Ratio	0.0400	0.0400
State of Wisconsin (to total assets), For Capital Adequacy Ratio	6.00%	6.00%
Total capital (to risk-weighted assets), Minimum Capital Adequacy with Capital Buffer	$ 178,717	$ 162,378
Tier I capital (to risk weighted assets), Minimum Capital Adequacy with Capital Buffer	144,676	131,449
Common Equity Tier I capital (to risk weighted assets) Minimum Capital Adequacy with Capital Buffer	$ 119,145	$ 108,252
Total capital (to risk-weighted assets), Minimum Capital Adequacy with Capital Buffer Ratio	10.50%	10.50%
Tier I capital (to risk weighted assets), Minimum Capital Adequacy with Capital Buffer Ratio	8.50%	8.50%
Common Equity Tier I capital (to risk weighted), Minimum Capital Adequacy with Capital Buffer Ratio	7.00%	7.00%
Total capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions	$ 170,207	$ 154,646
Tier I capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions	136,165	123,716
Common Equity Tier I capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions	110,634	100,520
Tier I capital (to average assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions	$ 108,119	$ 99,614
Total capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio	0.1000	0.1000
Tier I capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio	0.0800	0.0800
Common Equity Tier I capital (to risk-weighted) , To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio	0.0650	0.0650
Tier I capital (to average assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Ratio	0.0500	0.0500
Consolidated Waterstone Financial, Inc. [Member]
Actual and Required Capital Amounts and Ratios [Abstract]
Tier I capital (to risk-weighted assets)	$ 384,956
Tier I capital (to risk-weighted assets) Ratio	0.2260
Tier I capital (to risk-weighted assets), For Capital Adequacy Purposes	$ 102,201
Tier I capital (to risk-weighted assets), For Capital Adequacy Ratio	0.0600
Tier I capital (to risk weighted assets), Minimum Capital Adequacy with Capital Buffer	$ 144,784
Tier I capital (to risk weighted assets), Minimum Capital Adequacy with Capital Buffer Ratio	8.50%