LOANS HELD FOR INVESTMENT, NET - Allowance for Credit Losses Activity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Allowance for loan losses [Roll Forward]
Beginning balance	$ 98,200	$ 36,463	$ 41,461	$ 28,441
PCD Day 1			52,284
Provision (credit) for credit loss expense	(4,523)	6,060	8,126	14,072
Charge-offs	(1,033)	(36)	(5,308)	(42)
Recoveries	116	5	116	21
Ending balance	92,760	42,492	92,760	42,492
Non-accrual with No Allowance	35		35
Non-accrual with Allowance	28,251		28,251
Reserve			10,482
Interest income on non-accrual loans	0		0
Allowance for loan losses:
Individually evaluated for impairment					$ 6,474
Collectively evaluated for impairment					34,987
Total ending allowance balance	92,760	42,492	92,760	42,492	41,461
Loans:
Individually evaluated for impairment					17,069
Collectively evaluated for impairment					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)
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
Allowance for loan losses:
Total ending allowance balance					37,542
One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member]
Allowance for loan losses [Roll Forward]
Non-accrual with Allowance	4,933		4,933
Reserve			665
Commercial Real Estate and Commercial Mixed-Use [Member]
Allowance for loan losses [Roll Forward]
Non-accrual with No Allowance	35		35
Non-accrual with Allowance	9,117		9,117
Reserve			2,663
Real estate
Allowance for loan losses [Roll Forward]
Beginning balance	64,290	22,935	28,712	15,555
PCD Day 1			28,753
Provision (credit) for credit loss expense	(1,545)	6,074	7,514	13,446
Charge-offs	(583)	(36)	(841)	(42)
Recoveries	4	0	4	14
Ending balance	62,166	28,973	62,166	28,973
Allowance for loan losses:
Individually evaluated for impairment					0
Collectively evaluated for impairment					28,712
Total ending allowance balance	62,166	28,973	62,166	28,973	28,712
Loans:
Individually evaluated for impairment					4,567
Collectively evaluated for impairment					4,973,628
Total ending loans balance					4,978,195
Real estate | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance			(1,976)
Allowance for loan losses:
Total ending allowance balance					(1,976)
Real estate | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance			26,736
Allowance for loan losses:
Total ending allowance balance					26,736
Real estate | One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	5,133	645	644	269
PCD Day 1			2,220
Provision (credit) for credit loss expense	394	30	1,629	406
Charge-offs	(5)	(4)	(19)	(4)
Recoveries		0
Ending balance	5,522	671	5,522	671
Allowance for loan losses:
Individually evaluated for impairment					0
Collectively evaluated for impairment					644
Total ending allowance balance	5,522	671	5,522	671	644
Loans:
Individually evaluated for impairment					0
Collectively evaluated for impairment					184,989
Total ending loans balance					184,989
Real estate | One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member] | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance			1,048
Allowance for loan losses:
Total ending allowance balance					1,048
Real estate | One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance			1,692
Allowance for loan losses:
Total ending allowance balance					1,692
Real estate | Multifamily Residential and Residential Mixed-Use [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	10,421	14,283	17,016	10,142
PCD Day 1			3,292
Provision (credit) for credit loss expense	34	2,415	(1,363)	6,542
Charge-offs	(173)	(32)	(409)	(32)
Recoveries	3	0	3	14
Ending balance	10,285	16,666	10,285	16,666
Allowance for loan losses:
Individually evaluated for impairment					0
Collectively evaluated for impairment					17,016
Total ending allowance balance	10,285	16,666	10,285	16,666	17,016
Loans:
Individually evaluated for impairment					1,863
Collectively evaluated for impairment					2,756,880
Total ending loans balance					2,758,743
Real estate | Multifamily Residential and Residential Mixed-Use [Member] | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance			(8,254)
Allowance for loan losses:
Total ending allowance balance					(8,254)
Real estate | Multifamily Residential and Residential Mixed-Use [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance			8,762
Allowance for loan losses:
Total ending allowance balance					8,762
Real estate | Commercial Real Estate and Commercial Mixed-Use [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	44,837	6,336	9,059	3,900
PCD Day 1			23,124
Provision (credit) for credit loss expense	(3,232)	3,523	4,581	5,965
Charge-offs	(405)	0	(413)	(6)
Recoveries	1	0	1
Ending balance	41,201	9,859	41,201	9,859
Allowance for loan losses:
Individually evaluated for impairment					0
Collectively evaluated for impairment					9,059
Total ending allowance balance	41,201	9,859	41,201	9,859	9,059
Loans:
Individually evaluated for impairment					2,704
Collectively evaluated for impairment					1,875,463
Total ending loans balance					1,878,167
Real estate | Commercial Real Estate and Commercial Mixed-Use [Member] | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance			4,849
Allowance for loan losses:
Total ending allowance balance					4,849
Real estate | Commercial Real Estate and Commercial Mixed-Use [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance			13,908
Allowance for loan losses:
Total ending allowance balance					13,908
Real estate | ADC [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	3,899	1,671	1,993	1,244
PCD Day 1			117
Provision (credit) for credit loss expense	1,259	106	2,667	533
Charge-offs	0	0
Recoveries		0
Ending balance	5,158	1,777	5,158	1,777
Allowance for loan losses:
Individually evaluated for impairment					0
Collectively evaluated for impairment					1,993
Total ending allowance balance	5,158	1,777	5,158	1,777	1,993
Loans:
Individually evaluated for impairment					0
Collectively evaluated for impairment					156,296
Total ending loans balance					156,296
Real estate | ADC [Member] | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance			381
Allowance for loan losses:
Total ending allowance balance					381
Real estate | ADC [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance			2,374
Allowance for loan losses:
Total ending allowance balance					2,374
Commercial and industrial ("C&I") loans
Allowance for loan losses [Roll Forward]
Beginning balance		13,513	12,737	12,870
PCD Day 1			23,374
Provision (credit) for credit loss expense		(16)	272	625
Charge-offs		0	(4,462)
Recoveries		5	109	7
Ending balance	30,095	13,502	30,095	13,502
Allowance for loan losses:
Individually evaluated for impairment					6,474
Collectively evaluated for impairment					6,263
Total ending allowance balance	30,095	13,502	30,095	13,502	12,737
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)
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
Allowance for loan losses:
Total ending allowance balance					10,802
Commercial and industrial ("C&I"), including SBA and PPP loans
Allowance for loan losses [Roll Forward]
Beginning balance	33,378
Provision (credit) for credit loss expense	(2,947)
Charge-offs	(445)
Recoveries	109
Ending balance	30,095		30,095
Non-accrual with Allowance	14,109		14,109
Reserve			7,096
Allowance for loan losses:
Total ending allowance balance	30,095		30,095
Other loans
Allowance for loan losses [Roll Forward]
Beginning balance	532	15	12	16
PCD Day 1			157
Provision (credit) for credit loss expense	(31)	2	340	1
Charge-offs	(5)	0	(5)
Recoveries	3	0	3
Ending balance	499	17	499	17
Non-accrual with Allowance	92		92
Reserve			58
Allowance for loan losses:
Individually evaluated for impairment					0
Collectively evaluated for impairment					12
Total ending allowance balance	$ 499	$ 17	499	$ 17	12
Loans:
Individually evaluated for impairment					0
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)
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
Allowance for loan losses:
Total ending allowance balance					$ 4