LOANS HELD FOR INVESTMENT, NET - Allowance for Credit Losses Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for loan losses [Roll Forward]
Beginning balance	$ 41,461	$ 28,441	$ 21,782
PCD Day 1	52,284
Provision (credit) for credit loss expense	3,303	26,165	17,340
Charge-offs	(9,578)	(13,309)	(10,705)
Recoveries	302	164	24
Ending balance	83,853	41,461	28,441
Non-accrual with No Allowance	1,649
Non-accrual with Allowance	38,658
Reserve	19,409
Allowance for loan losses:
Individually evaluated for impairment	22,300	6,474
Collectively evaluated for impairment	41,400	34,987
Total ending allowance balance	83,853	41,461	28,441
Loans:
Individually evaluated for impairment	51,400	17,069
Collectively evaluated for impairment	8,980,000	5,604,975
Total ending loans balance		5,622,044
Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	(3,919)
Ending balance		(3,919)
Allowance for loan losses:
Total ending allowance balance		(3,919)
Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	37,542
Ending balance		37,542
Allowance for loan losses:
Total ending allowance balance		37,542
Total real estate loans
Allowance for loan losses [Roll Forward]
Beginning balance	28,712	15,555	17,818
PCD Day 1	28,753
Provision (credit) for credit loss expense	(4,077)	16,234	(2,034)
Charge-offs	(3,817)	(3,207)	(250)
Recoveries	176	130	21
Ending balance	47,771	28,712	15,555
Allowance for loan losses:
Collectively evaluated for impairment		28,712
Total ending allowance balance	47,771	28,712	15,555
Loans:
Individually evaluated for impairment		4,567
Collectively evaluated for impairment		4,973,628
Total ending loans balance		4,978,195
Total real estate loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	(1,976)
Ending balance		(1,976)
Allowance for loan losses:
Total ending allowance balance		(1,976)
Total real estate loans | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	26,736
Ending balance		26,736
Allowance for loan losses:
Total ending allowance balance		26,736
One-to-four family residential and cooperative/condominium apartment
Allowance for loan losses [Roll Forward]
Beginning balance	644	269	198
PCD Day 1	2,220
Provision (credit) for credit loss expense	1,975	386	86
Charge-offs	(20)	(11)	(22)
Recoveries	65		7
Ending balance	5,932	644	269
Non-accrual with Allowance	7,623
Reserve	1,278
Allowance for loan losses:
Collectively evaluated for impairment		644
Total ending allowance balance	5,932	644	269
Loans:
Collectively evaluated for impairment		184,989
Total ending loans balance		184,989
One-to-four family residential and cooperative/condominium apartment | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	1,048
Ending balance		1,048
Allowance for loan losses:
Total ending allowance balance		1,048
One-to-four family residential and cooperative/condominium apartment | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	1,692
Ending balance		1,692
Allowance for loan losses:
Total ending allowance balance		1,692
Multifamily residential and residential mixed-use
Allowance for loan losses [Roll Forward]
Beginning balance	17,016	10,142	13,446
PCD Day 1	3,292
Provision (credit) for credit loss expense	(3,921)	9,934	(3,233)
Charge-offs	(391)	(3,190)	(83)
Recoveries	74	130	12
Ending balance	7,816	17,016	10,142
Allowance for loan losses:
Collectively evaluated for impairment		17,016
Total ending allowance balance	7,816	17,016	10,142
Loans:
Individually evaluated for impairment		1,863
Collectively evaluated for impairment		2,756,880
Total ending loans balance		2,758,743
Multifamily residential and residential mixed-use | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	(8,254)
Ending balance		(8,254)
Allowance for loan losses:
Total ending allowance balance		(8,254)
Multifamily residential and residential mixed-use | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	8,762
Ending balance		8,762
Allowance for loan losses:
Total ending allowance balance		8,762
Acquisition, development, and construction ("ADC")
Allowance for loan losses [Roll Forward]
Beginning balance	1,993	1,244	397
PCD Day 1	117
Provision (credit) for credit loss expense	2,366	749	847
Ending balance	4,857	1,993	1,244
Allowance for loan losses:
Collectively evaluated for impairment		1,993
Total ending allowance balance	4,857	1,993	1,244
Loans:
Collectively evaluated for impairment		156,296
Total ending loans balance		156,296
Acquisition, development, and construction ("ADC") | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	381
Ending balance		381
Allowance for loan losses:
Total ending allowance balance		381
Acquisition, development, and construction ("ADC") | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	2,374
Ending balance		2,374
Allowance for loan losses:
Total ending allowance balance		2,374
Commercial real estate ("CRE")
Allowance for loan losses [Roll Forward]
Beginning balance	9,059	3,900	3,777
PCD Day 1	23,124
Provision (credit) for credit loss expense	(4,497)	5,165	266
Charge-offs	(3,406)	(6)	(145)
Recoveries	37		2
Ending balance	29,166	9,059	3,900
Non-accrual with No Allowance	1,301
Non-accrual with Allowance	3,752
Reserve	797
Allowance for loan losses:
Collectively evaluated for impairment		9,059
Total ending allowance balance	29,166	9,059	3,900
Loans:
Individually evaluated for impairment		2,704
Collectively evaluated for impairment		1,875,463
Total ending loans balance		1,878,167
Commercial real estate ("CRE") | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	4,849
Ending balance		4,849
Allowance for loan losses:
Total ending allowance balance		4,849
Commercial real estate ("CRE") | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	13,908
Ending balance		13,908
Allowance for loan losses:
Total ending allowance balance		13,908
Commercial and Industrial ("C&I") Loans
Allowance for loan losses [Roll Forward]
Beginning balance	12,737	12,870	3,946
PCD Day 1	23,374
Provision (credit) for credit loss expense	6,016	9,928	19,368
Charge-offs	(4,984)	(10,095)	(10,447)
Recoveries	123	34	3
Ending balance	35,331	12,737	12,870
Non-accrual with No Allowance	348
Non-accrual with Allowance	26,918
Reserve	16,973
Allowance for loan losses:
Individually evaluated for impairment		6,474
Collectively evaluated for impairment		6,263
Total ending allowance balance	35,331	12,737	12,870
Loans:
Individually evaluated for impairment		12,502
Collectively evaluated for impairment		629,031
Total ending loans balance		641,533
Commercial and Industrial ("C&I") Loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	(1,935)
Ending balance		(1,935)
Allowance for loan losses:
Total ending allowance balance		(1,935)
Commercial and Industrial ("C&I") Loans | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	10,802
Ending balance		10,802
Allowance for loan losses:
Total ending allowance balance		10,802
Other Loans
Allowance for loan losses [Roll Forward]
Beginning balance	12	16	18
PCD Day 1	157
Provision (credit) for credit loss expense	1,364	3	6
Charge-offs	(777)	(7)	(8)
Recoveries	3
Ending balance	751	12	16
Non-accrual with Allowance	365
Reserve	361
Allowance for loan losses:
Collectively evaluated for impairment		12
Total ending allowance balance	751	12	$ 16
Loans:
Collectively evaluated for impairment		2,316
Total ending loans balance		2,316
Other Loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance	(8)
Ending balance		(8)
Allowance for loan losses:
Total ending allowance balance		(8)
Other Loans | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance	$ 4
Ending balance		4
Allowance for loan losses:
Total ending allowance balance		$ 4