LOANS HELD FOR INVESTMENT, NET - Credit Quality Indicators (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	$ 9,249,849	$ 9,244,661
2022	493,979
2021	1,817,960	1,839,501
2020	1,389,448	1,502,001
2019	1,217,009	1,289,329
2018	696,107	726,725
2017 and Prior	2,945,539	878,430
2016 and Prior		2,356,918
Revolving	632,210	588,432
Revolving-Term	45,390	46,426
Total Loans	9,237,642	9,227,762
Pass
Credit Risk Profile of Real Estate Loans [Abstract]
2022	489,398
2021	1,806,517	1,828,115
2020	1,365,302	1,473,478
2019	1,106,603	1,174,655
2018	568,972	606,030
2017 and Prior	2,595,993	752,529
2016 and Prior		2,114,512
Revolving	606,532	552,538
Revolving-Term	29,410	29,902
Total Loans	8,568,727	8,531,759
Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
2022	4,581
2021	5,289	6,003
2020	14,051	15,891
2019	51,769	54,365
2018	26,016	21,926
2017 and Prior	62,273	23,775
2016 and Prior		45,900
Revolving	10,157	4,071
Revolving-Term	2,091	2,033
Total Loans	176,227	173,964
Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2021	5,658	4,833
2020	10,095	11,011
2019	49,734	50,235
2018	100,344	97,994
2017 and Prior	276,343	91,019
2016 and Prior		196,506
Revolving	15,521	30,823
Revolving-Term	13,889	14,491
Total Loans	471,584	496,912
Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
2021	496	550
2020		1,621
2019	8,903	10,074
2018	775	775
2017 and Prior	10,930	11,107
Revolving		1,000
Total Loans	21,104	25,127
Total real estate loans
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	8,316,633	8,294,204
One-to-four family residential and cooperative/condominium apartment
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	669,099	669,282
2022	54,932
2021	128,132	129,679
2020	77,562	89,096
2019	66,898	82,568
2018	69,590	76,726
2017 and Prior	209,761	80,365
2016 and Prior		145,946
Revolving	49,414	50,724
Revolving-Term	12,810	14,178
Total Loans	669,099	669,282
One-to-four family residential and cooperative/condominium apartment | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
2022	54,932
2021	128,132	129,679
2020	76,520	86,028
2019	65,332	80,195
2018	68,429	75,354
2017 and Prior	193,054	77,829
2016 and Prior		129,276
Revolving	48,569	49,878
Revolving-Term	11,190	12,537
Total Loans	646,158	640,776
One-to-four family residential and cooperative/condominium apartment | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
2020		1,124
2019	334	335
2018	748	752
2017 and Prior	1,810	334
2016 and Prior		2,158
Revolving	845	846
Revolving-Term	742	747
Total Loans	4,479	6,296
One-to-four family residential and cooperative/condominium apartment | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2020	1,042	1,944
2019	1,232	2,038
2018	413	597
2017 and Prior	14,897	2,202
2016 and Prior		14,512
Revolving-Term	878	894
Total Loans	18,462	22,187
One-to-four family residential and cooperative/condominium apartment | Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
2018		23
Total Loans		23
Multifamily residential and residential mixed-use
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	3,371,267	3,356,346
2022	235,590
2021	587,949	590,462
2020	342,620	353,747
2019	484,453	505,089
2018	176,769	183,616
2017 and Prior	1,528,494	398,804
2016 and Prior		1,309,248
Revolving	14,567	14,555
Revolving-Term	825	825
Total Loans	3,371,267	3,356,346
Multifamily residential and residential mixed-use | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
2022	235,590
2021	587,949	590,462
2020	330,142	341,206
2019	426,898	455,277
2018	134,833	151,226
2017 and Prior	1,300,004	332,749
2016 and Prior		1,145,609
Revolving	14,567	12,277
Revolving-Term	825	825
Total Loans	3,030,808	3,029,631
Multifamily residential and residential mixed-use | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
2020	10,985	11,040
2019	22,251	14,486
2018	4,216
2017 and Prior	29,032	11,817
2016 and Prior		26,252
Total Loans	66,484	63,595
Multifamily residential and residential mixed-use | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2020	1,493	1,501
2019	35,304	35,326
2018	37,720	32,390
2017 and Prior	199,458	54,238
2016 and Prior		137,387
Revolving		2,278
Total Loans	273,975	263,120
Commercial real estate ("CRE")
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	3,946,918	3,945,948
2022	166,352
2021	874,382	882,483
2020	803,263	851,450
2019	561,723	575,675
2018	362,875	370,839
2017 and Prior	1,125,632	341,690
2016 and Prior		874,439
Revolving	46,693	43,183
Revolving-Term	5,998	6,188
Total Loans	3,946,918	3,945,947
Commercial real estate ("CRE") | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
2022	166,352
2021	864,565	872,049
2020	800,777	848,694
2019	525,522	529,182
2018	298,706	306,360
2017 and Prior	1,038,627	298,904
2016 and Prior		815,238
Revolving	46,693	43,183
Revolving-Term	5,998	6,188
Total Loans	3,747,240	3,719,798
Commercial real estate ("CRE") | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
2021	5,289	6,003
2020	881	1,024
2019	28,819	39,305
2018	18,877	18,983
2017 and Prior	30,315	11,039
2016 and Prior		17,438
Total Loans	84,181	93,792
Commercial real estate ("CRE") | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2021	4,528	4,431
2020	1,605	1,732
2019	7,276	7,082
2018	45,292	45,496
2017 and Prior	56,690	31,747
2016 and Prior		41,763
Total Loans	115,391	132,251
Commercial real estate ("CRE") | Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
2019	106	106
Total Loans	106	106
Acquisition, development, and construction
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	329,349	322,628
2022	8,648
2021	160,508	142,123
2020	64,407	77,427
2019	40,083	56,885
2018	33,283	36,956
2017 and Prior	6,263	6,809
2016 and Prior		774
Revolving	14,997	1,066
Revolving-Term	1,160	588
Total Loans	329,349	322,628
Acquisition, development, and construction | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
2022	8,648
2021	159,843	142,123
2020	64,407	76,259
2019	40,083	56,885
2018	19,783	23,456
2017 and Prior	6,263	6,809
2016 and Prior		774
Revolving	14,997	1,066
Revolving-Term	1,160	588
Total Loans	315,184	307,960
Acquisition, development, and construction | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
2020		1,078
Total Loans		1,078
Acquisition, development, and construction | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2021	665
2020		90
2018	13,500	13,500
Total Loans	14,165	13,590
Commercial and Industrial ("C&I") Loans
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	921,009	933,559
2022	28,457
2021	66,989	94,754
2020	101,596	130,281
2019	63,852	69,112
2018	53,590	58,588
2017 and Prior	75,389	50,762
2016 and Prior		26,511
Revolving	506,539	478,904
Revolving-Term	24,597	24,647
Total Loans	921,009	933,559
Commercial and Industrial ("C&I") Loans | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
2022	23,876
2021	66,028	93,802
2020	93,456	121,291
2019	48,768	53,116
2018	47,221	49,634
2017 and Prior	58,045	36,238
2016 and Prior		23,615
Revolving	481,706	446,134
Revolving-Term	10,237	9,764
Total Loans	829,337	833,594
Commercial and Industrial ("C&I") Loans | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
2022	4,581
2020	2,185	1,625
2019	365	239
2018	2,175	2,191
2017 and Prior	1,116	585
2016 and Prior		52
Revolving	9,312	3,225
Revolving-Term	1,349	1,286
Total Loans	21,083	9,203
Commercial and Industrial ("C&I") Loans | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2021	465	402
2020	5,955	5,744
2019	5,922	5,789
2018	3,419	6,011
2017 and Prior	5,298	2,832
2016 and Prior		2,844
Revolving	15,521	28,545
Revolving-Term	13,011	13,597
Total Loans	49,591	65,764
Commercial and Industrial ("C&I") Loans | Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
2021	496	550
2020		1,621
2019	8,797	9,968
2018	775	752
2017 and Prior	10,930	11,107
Revolving		1,000
Total Loans	20,998	24,998
Other Loans
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	12,207	16,898
Other Loans | Credit Risk Profile
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	12,207
Other Loans | Performing
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		16,533
Other Loans | Performing | Credit Risk Profile
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	12,124
Other Loans | Non-Accrual
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		$ 365
Other Loans | Non-Accrual | Credit Risk Profile
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	$ 83