LOANS HELD FOR INVESTMENT, NET - Past Due Status (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	$ 9,249,849	$ 9,244,661
Non-accrual	35,962	40,307
Aggregate outstanding balance	1,200	3,000
Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	65,182	116,696
30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	27,116	61,242
60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	924	12,146
Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	1,180	3,001
Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	9,184,667	9,127,965
Total real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	8,316,633	8,294,204
Non-accrual	10,878	12,676
Total real estate loans | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	35,162	77,109
Total real estate loans | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	23,258	57,385
Total real estate loans | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	685	5,103
Total real estate loans | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	341	1,945
Total real estate loans | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	8,281,471	8,217,095
One-to-four family residential and cooperative/condominium apartment
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	669,099	669,282
Non-accrual	5,241	7,623
One-to-four family residential and cooperative/condominium apartment | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	10,487	13,739
One-to-four family residential and cooperative/condominium apartment | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	4,220	3,294
One-to-four family residential and cooperative/condominium apartment | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	685	877
One-to-four family residential and cooperative/condominium apartment | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	341	1,945
One-to-four family residential and cooperative/condominium apartment | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	658,612	655,543
Multifamily residential and residential mixed-use
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	3,371,267	3,356,346
Multifamily residential and residential mixed-use | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	6,545	34,322
Multifamily residential and residential mixed-use | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	6,545	30,983
Multifamily residential and residential mixed-use | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	0	3,339
Multifamily residential and residential mixed-use | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	3,364,722	3,322,024
Commercial real estate ("CRE")
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	3,946,918	3,945,948
Non-accrual	4,972	5,053
Commercial real estate ("CRE") | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	17,465	29,048
Commercial real estate ("CRE") | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	12,493	23,108
Commercial real estate ("CRE") | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	0	887
Commercial real estate ("CRE") | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	3,929,453	3,916,900
Acquisition, development, and construction
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	329,349	322,628
Non-accrual	665
Acquisition, development, and construction | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	665
Acquisition, development, and construction | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	0
Acquisition, development, and construction | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	0
Acquisition, development, and construction | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	0
Acquisition, development, and construction | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	328,684	322,628
Commercial and Industrial ("C&I") Loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	921,009	933,559
Non-accrual	25,000	27,266
Commercial and Industrial ("C&I") Loans | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	29,767	39,115
Commercial and Industrial ("C&I") Loans | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	3,689	3,753
Commercial and Industrial ("C&I") Loans | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	239	7,040
Commercial and Industrial ("C&I") Loans | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	839	1,056
Commercial and Industrial ("C&I") Loans | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	891,242	894,444
Other Loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	12,207	16,898
Non-accrual	84	365
Other Loans | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	253	472
Other Loans | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	169	104
Other Loans | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	0	3
Other Loans | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	0
Other Loans | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Principal balances outstanding	$ 11,954	$ 16,426