LOANS HELD FOR INVESTMENT, NET - Allowance for Credit Losses Activity (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Allowance for loan losses [Roll Forward]
Beginning balance	$ 83,853,000	$ 41,461,000	$ 41,461,000
PCD Day 1		52,284,000
(Credit) provision for credit losses	(1,654,000)	12,649,000
Charge-offs	(2,638,000)	(4,275,000)
Recoveries	54,000
Ending balance	79,615,000	98,200,000	83,853,000
Amortized cost basis of loans on non-accrual status
Non-accrual with No Allowance	2,253,000		1,649,000
Non-accrual with Allowance	33,709,000		38,658,000
Reserve	16,623,000		19,409,000
Interest income on non-accrual loans held for investment
Interest income on non-accrual loans	0	0
Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		(3,919,000)	(3,919,000)
Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		37,542,000	37,542,000
Total real estate loans
Allowance for loan losses [Roll Forward]
Beginning balance	47,771,000	28,712,000	28,712,000
PCD Day 1		28,753,000
(Credit) provision for credit losses	(2,781,000)	9,059,000
Charge-offs		(258,000)
Recoveries	2,000
Ending balance	44,992,000	64,290,000	47,771,000
Total real estate loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		(1,976,000)	(1,976,000)
Total real estate loans | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		26,736,000	26,736,000
One-to-four family residential and cooperative/condominium apartment
Allowance for loan losses [Roll Forward]
Beginning balance	5,932,000	644,000	644,000
PCD Day 1		2,220,000
(Credit) provision for credit losses	(1,404,000)	1,235,000
Charge-offs		(14,000)
Ending balance	4,528,000	5,133,000	5,932,000
Amortized cost basis of loans on non-accrual status
Non-accrual with Allowance	5,241,000		7,623,000
Reserve	151,000		1,278,000
One-to-four family residential and cooperative/condominium apartment | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		1,048,000	1,048,000
One-to-four family residential and cooperative/condominium apartment | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		1,692,000	1,692,000
Multifamily residential and residential mixed-use
Allowance for loan losses [Roll Forward]
Beginning balance	7,816,000	17,016,000	17,016,000
PCD Day 1		3,292,000
(Credit) provision for credit losses	(757,000)	(1,397,000)
Charge-offs		(236,000)
Recoveries	2,000
Ending balance	7,061,000	10,421,000	7,816,000
Multifamily residential and residential mixed-use | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		(8,254,000)	(8,254,000)
Multifamily residential and residential mixed-use | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		8,762,000	8,762,000
Acquisition, development, and construction
Allowance for loan losses [Roll Forward]
Beginning balance	4,857,000	1,993,000	1,993,000
PCD Day 1		117,000
(Credit) provision for credit losses	(99,000)	1,408,000
Ending balance	4,758,000	3,899,000	4,857,000
Amortized cost basis of loans on non-accrual status
Non-accrual with No Allowance	665,000
Acquisition, development, and construction | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		381,000	381,000
Acquisition, development, and construction | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		2,374,000	2,374,000
Commercial real estate ("CRE")
Allowance for loan losses [Roll Forward]
Beginning balance	29,166,000	9,059,000	9,059,000
PCD Day 1		23,124,000
(Credit) provision for credit losses	(521,000)	7,813,000
Charge-offs		(8,000)
Ending balance	28,645,000	44,837,000	29,166,000
Amortized cost basis of loans on non-accrual status
Non-accrual with No Allowance	1,254,000		1,301,000
Non-accrual with Allowance	3,719,000		3,752,000
Reserve	1,564,000		797,000
Commercial real estate ("CRE") | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		4,849,000	4,849,000
Commercial real estate ("CRE") | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		13,908,000	13,908,000
Commercial and Industrial ("C&I") Loans
Allowance for loan losses [Roll Forward]
Beginning balance	35,331,000	12,737,000	12,737,000
PCD Day 1		23,374,000
(Credit) provision for credit losses	1,516,000	3,219,000
Charge-offs	(2,635,000)	(4,017,000)
Recoveries	51,000
Ending balance	34,263,000	33,378,000	35,331,000
Amortized cost basis of loans on non-accrual status
Non-accrual with No Allowance	334,000		348,000
Non-accrual with Allowance	24,666,000		26,918,000
Reserve	14,829,000		16,973,000
Commercial and Industrial ("C&I") Loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		(1,935,000)	(1,935,000)
Commercial and Industrial ("C&I") Loans | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		10,802,000	10,802,000
Other Loans
Allowance for loan losses [Roll Forward]
Beginning balance	751,000	12,000	12,000
PCD Day 1		157,000
(Credit) provision for credit losses	(389,000)	371,000
Charge-offs	(3,000)
Recoveries	1,000
Ending balance	360,000	532,000	751,000
Amortized cost basis of loans on non-accrual status
Non-accrual with Allowance	83,000		365,000
Reserve	$ 79,000		361,000
Other Loans | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses [Roll Forward]
Beginning balance		(8,000)	(8,000)
Other Loans | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses [Roll Forward]
Beginning balance		$ 4,000	$ 4,000