LOANS - Loans Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,218,314	$ 6,230,977
Allowance for loan losses	(40,657)	(36,001)
Loans held for investment, net	6,177,657	6,194,976
Multifamily residential \| Permanent mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,058,869	3,985,981
Single family residential \| Permanent mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,930,831	2,021,320
Commercial real estate \| Permanent mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	205,657	203,134
Construction and land loans \| Permanent mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	22,857	20,442
Land, Construction and NM \| Non-Mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 100	$ 100

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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