STOCKHOLDERS' EQUITY AND REGULATORY CAPITAL - Schedule of Capital Position (Details) $ in Thousands	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Capital Unit [Line Items]
Total Capital (to risk-weighted assets), Consolidated Capital Amount	$ 2,219,920	$ 1,610,964
Tier 1 Capital (to risk-weighted assets), Consolidated Capital Amount	1,910,195	1,528,398
Common Equity Tier 1 Capital (to risk-weighted assets), Consolidated Bank Capital Amount	1,910,195	1,463,398
Tier 1 Capital (to adjusted tangible assets), Consolidated Capital Amount	$ 1,910,195	$ 1,528,398
Total Capital (to risk-weighted assets), Consolidated Capital Percent	0.1420	0.1559
Tier 1 Capital (to risk-weighted assets), Consolidated Capital Percent	0.1222	0.1479
Common Equity Tier 1 Capital (to risk-weighted assets), Consolidated Capital Percent	12.22%	14.16%
Tier 1 Leverage Capital , Consolidated Capital Percent	0.0979	0.1024
Total Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Amount	$ 1,250,689	$ 826,839
Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Amount	938,017	620,129
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Amount	703,512	465,097
Tier 1 Leverage Capital, Minimum For Capital Adequacy Purposes Amount	$ 780,333	$ 597,179
Total Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Percentage	0.0800	0.0800
Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Percentage	0.0600	0.0600
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Percentage	4.50%	4.50%
Tier 1 Leverage Capital, Minimum For Capital Adequacy Purposes Percentage	0.0400	0.0400
Total Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,563,361	$ 1,033,548
Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	1,250,689	826,839
Common Equity Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	1,016,185	671,806
Tier 1 Leverage Capital, To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	$ 975,416	$ 746,473
Total Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	0.1000	0.1000
Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	0.0800	0.0800
Common Equity Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	6.50%	6.50%
Tier 1 Leverage Capital, To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	0.0500	0.0500
Wilmington Savings Fund Society, FSB
Capital Unit [Line Items]
Total Capital (to risk-weighted assets), Consolidated Capital Amount	$ 2,157,846	$ 1,639,708
Tier 1 Capital (to risk-weighted assets), Consolidated Capital Amount	2,003,779	1,557,142
Common Equity Tier 1 Capital (to risk-weighted assets), Consolidated Bank Capital Amount	2,003,779	1,557,142
Tier 1 Capital (to adjusted tangible assets), Consolidated Capital Amount	$ 2,003,779	$ 1,557,142
Total Capital (to risk-weighted assets), Consolidated Capital Percent	0.1384	0.1591
Tier 1 Capital (to risk-weighted assets), Consolidated Capital Percent	0.1286	0.1511
Common Equity Tier 1 Capital (to risk-weighted assets), Consolidated Capital Percent	12.86%	15.11%
Tier 1 Leverage Capital , Consolidated Capital Percent	0.1029	0.1044
Total Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Amount	$ 1,246,886	$ 824,687
Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Amount	935,165	618,515
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Amount	701,373	463,886
Tier 1 Leverage Capital, Minimum For Capital Adequacy Purposes Amount	$ 779,288	$ 596,711
Total Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Percentage	0.0800	0.0800
Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Percentage	0.0600	0.0600
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum For Capital Adequacy Purposes Percentage	4.50%	4.50%
Tier 1 Leverage Capital, Minimum For Capital Adequacy Purposes Percentage	0.0400	0.0400
Total Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,558,608	$ 1,030,858
Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	1,246,886	824,687
Common Equity Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	1,013,095	670,058
Tier 1 Leverage Capital, To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount	$ 974,110	$ 745,889
Total Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	0.1000	0.1000
Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	0.0800	0.0800
Common Equity Tier 1 Capital (to risk-weighted assets), To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	6.50%	6.50%
Tier 1 Leverage Capital, To Be Well-Capitalized Under Prompt Corrective Action Provisions Percentage	0.0500	0.0500