LOANS HELD FOR INVESTMENT, NET - Past Due Status (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	$ 10,850,611,000	$ 10,566,831,000
Non-accrual	23,320,000	34,237,000
Accruing Loans 90 Days or More Past Due	0	0
Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	58,331,000	58,496,000
30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	22,961,000	23,517,000
60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	12,050,000	742,000
Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	10,792,280,000	10,508,335,000
Business loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	2,271,768,000	2,211,857,000
Non-accrual	19,555,000	27,787,000
Business loans | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	37,399,000	34,389,000
Business loans | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	16,693,000	5,861,000
Business loans | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	1,151,000	741,000
Business loans | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	2,234,369,000	2,177,468,000
One-to-four family residential and cooperative/condominium apartment
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	892,869,000	773,321,000
Non-accrual	2,874,000	3,203,000
One-to-four family residential and cooperative/condominium apartment | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	5,957,000	3,889,000
One-to-four family residential and cooperative/condominium apartment | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	439,000	686,000
One-to-four family residential and cooperative/condominium apartment | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	2,644,000
One-to-four family residential and cooperative/condominium apartment | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	886,912,000	769,432,000
Multifamily residential and residential mixed-use
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	4,102,024,000	4,026,826,000
Non-accrual	0
Multifamily residential and residential mixed-use | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	3,794,000	4,817,000
Multifamily residential and residential mixed-use | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	2,976,000	4,817,000
Multifamily residential and residential mixed-use | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	818,000
Multifamily residential and residential mixed-use | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	0
Multifamily residential and residential mixed-use | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	4,098,230,000	4,022,009,000
Non-owner-occupied commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	3,374,281,000	3,317,485,000
Non-owner-occupied commercial real estate | Total real estate loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	3,374,281,000	3,317,485,000
Non-accrual	15,000	2,491,000
Non-owner-occupied commercial real estate | Total real estate loans | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	9,653,000	14,380,000
Non-owner-occupied commercial real estate | Total real estate loans | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	2,851,000	11,889,000
Non-owner-occupied commercial real estate | Total real estate loans | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	6,787,000
Non-owner-occupied commercial real estate | Total real estate loans | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	3,364,628,000	3,303,105,000
Acquisition, development, and construction ("ADC")
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	203,402,000	229,663,000
Non-accrual	657,000	657,000
Acquisition, development, and construction ("ADC") | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	1,307,000	657,000
Acquisition, development, and construction ("ADC") | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	0
Acquisition, development, and construction ("ADC") | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	650,000
Acquisition, development, and construction ("ADC") | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	0
Acquisition, development, and construction ("ADC") | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	202,095,000	229,006,000
Other Loans
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	6,267,000	7,679,000
Non-accrual	219,000	99,000
Other Loans | Total Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	221,000	364,000
Other Loans | 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	2,000	264,000
Other Loans | 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	0	1,000
Other Loans | Loans 90 Days or More Past Due and Still Accruing Interest
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	0
Other Loans | Current
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	$ 6,046,000	$ 7,315,000