LOANS HELD FOR INVESTMENT, NET - Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	$ 9,244,661	$ 5,622,044
2021	1,839,501
2020	1,502,001
2019	1,289,329
2018	726,725
2017	878,430
2016 and Prior	2,356,918
Revolving	588,432
Revolving-Term	46,426
Total Loans	9,227,762
Pass
Credit Risk Profile of Real Estate Loans [Abstract]
2021	1,828,115
2020	1,473,478
2019	1,174,655
2018	606,030
2017	752,529
2016 and Prior	2,114,512
Revolving	552,538
Revolving-Term	29,902
Total Loans	8,531,759
Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
2021	6,003
2020	15,891
2019	54,365
2018	21,926
2017	23,775
2016 and Prior	45,900
Revolving	4,071
Revolving-Term	2,033
Total Loans	173,964
Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2021	4,833
2020	11,011
2019	50,235
2018	97,994
2017	91,019
2016 and Prior	196,506
Revolving	30,823
Revolving-Term	14,491
Total Loans	496,912
Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
2021	550
2020	1,621
2019	10,074
2018	775
2017	11,107
Revolving	1,000
Total Loans	25,127
Total real estate loans
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	8,294,204	4,978,195
Total real estate loans | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		4,681,059
Total real estate loans | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		83,761
Total real estate loans | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		213,375
One-to-four family residential and cooperative/condominium apartment
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	669,282	184,989
2021	129,679
2020	89,096
2019	82,568
2018	76,726
2017	80,365
2016 and Prior	145,946
Revolving	50,724
Revolving-Term	14,178
Total Loans	669,282
One-to-four family residential and cooperative/condominium apartment | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		183,293
2021	129,679
2020	86,028
2019	80,195
2018	75,354
2017	77,829
2016 and Prior	129,276
Revolving	49,878
Revolving-Term	12,537
Total Loans	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	335
2018	752
2017	334
2016 and Prior	2,158
Revolving	846
Revolving-Term	747
Total Loans	6,296
One-to-four family residential and cooperative/condominium apartment | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		1,696
2020	1,944
2019	2,038
2018	597
2017	2,202
2016 and Prior	14,512
Revolving-Term	894
Total Loans	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	3,356,346	2,758,743
2021	590,462
2020	353,747
2019	505,089
2018	183,616
2017	398,804
2016 and Prior	1,309,248
Revolving	14,555
Revolving-Term	825
Total Loans	3,356,346
Multifamily residential and residential mixed-use | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		2,523,258
2021	590,462
2020	341,206
2019	455,277
2018	151,226
2017	332,749
2016 and Prior	1,145,609
Revolving	12,277
Revolving-Term	825
Total Loans	3,029,631
Multifamily residential and residential mixed-use | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		56,400
2020	11,040
2019	14,486
2017	11,817
2016 and Prior	26,252
Total Loans	63,595
Multifamily residential and residential mixed-use | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		179,085
2020	1,501
2019	35,326
2018	32,390
2017	54,238
2016 and Prior	137,387
Revolving	2,278
Total Loans	263,120
Commercial real estate ("CRE")
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	3,945,948	1,878,167
2021	882,483
2020	851,450
2019	575,675
2018	370,839
2017	341,690
2016 and Prior	874,439
Revolving	43,183
Revolving-Term	6,188
Total Loans	3,945,947
Commercial real estate ("CRE") | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		1,831,712
2021	872,049
2020	848,694
2019	529,182
2018	306,360
2017	298,904
2016 and Prior	815,238
Revolving	43,183
Revolving-Term	6,188
Total Loans	3,719,798
Commercial real estate ("CRE") | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		13,861
2021	6,003
2020	1,024
2019	39,305
2018	18,983
2017	11,039
2016 and Prior	17,438
Total Loans	93,792
Commercial real estate ("CRE") | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		32,594
2021	4,431
2020	1,732
2019	7,082
2018	45,496
2017	31,747
2016 and Prior	41,763
Total Loans	132,251
Commercial real estate ("CRE") | Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
2019	106
Total Loans	106
Acquisition, development, and construction ("ADC")
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	322,628	156,296
2021	142,123
2020	77,427
2019	56,885
2018	36,956
2017	6,809
2016 and Prior	774
Revolving	1,066
Revolving-Term	588
Total Loans	322,628
Acquisition, development, and construction ("ADC") | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		142,796
2021	142,123
2020	76,259
2019	56,885
2018	23,456
2017	6,809
2016 and Prior	774
Revolving	1,066
Revolving-Term	588
Total Loans	307,960
Acquisition, development, and construction ("ADC") | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		13,500
2020	1,078
Total Loans	1,078
Acquisition, development, and construction ("ADC") | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
2020	90
2018	13,500
Total Loans	13,590
Commercial and Industrial ("C&I") Loans
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	933,559	641,533
2021	94,754
2020	130,281
2019	69,112
2018	58,588
2017	50,762
2016 and Prior	26,511
Revolving	478,904
Revolving-Term	24,647
Total Loans	933,559
Commercial and Industrial ("C&I") Loans | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		613,691
2021	93,802
2020	121,291
2019	53,116
2018	49,634
2017	36,238
2016 and Prior	23,615
Revolving	446,134
Revolving-Term	9,764
Total Loans	833,594
Commercial and Industrial ("C&I") Loans | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		2,131
2020	1,625
2019	239
2018	2,191
2017	585
2016 and Prior	52
Revolving	3,225
Revolving-Term	1,286
Total Loans	9,203
Commercial and Industrial ("C&I") Loans | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		13,315
2021	402
2020	5,744
2019	5,789
2018	6,011
2017	2,832
2016 and Prior	2,844
Revolving	28,545
Revolving-Term	13,597
Total Loans	65,764
Commercial and Industrial ("C&I") Loans | Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		12,396
2021	550
2020	1,621
2019	9,968
2018	752
2017	11,107
Revolving	1,000
Total Loans	24,998
Commercial and Industrial ("C&I") Loans | Total real estate loans
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		5,619,728
Commercial and Industrial ("C&I") Loans | Total real estate loans | Pass
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		5,294,750
Commercial and Industrial ("C&I") Loans | Total real estate loans | Special Mention
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		85,892
Commercial and Industrial ("C&I") Loans | Total real estate loans | Substandard
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		226,690
Commercial and Industrial ("C&I") Loans | Total real estate loans | Doubtful
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		12,396
Other Loans
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	16,898	2,316
Other Loans | Credit Risk Profile
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	16,898
Other Loans | Performing
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		2,315
Other Loans | Performing | Credit Risk Profile
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	16,533
Other Loans | Non-Accrual
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding		$ 1
Other Loans | Non-Accrual | Credit Risk Profile
Credit Risk Profile of Real Estate Loans [Abstract]
Principal balances outstanding	$ 365