LOANS - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) Contract	Dec. 31, 2019 USD ($) Loan Contract	Dec. 31, 2018 USD ($) Contract
Financing Receivable Recorded Investment Past Due [Line Items]
Loans held for sale, at lower of cost or fair value	$ 18,520,000	$ 14,667,000
Gain (loss) on loans held for sale at lower of cost or fair value	7,426,000	(10,000)	$ (4,392,000)
Impaired non-accrual loans	11,410,000	28,881,000
Transfer of loans to loans held for sale	367,477,000	15,064,000	$ 137,317,000
Charge-off	5,900,000
Impaired non-accrual loans performing troubled debt restructured	201,000	2,400,000
Allowance allocated to troubled debt restructured loans	3,000	2,800,000
Allowance allocated to non accrual loans	0	$ 2,700,000
Loan receivable, validate risk ratings performed for large sample or new lending to existing relationships	1,000,000
Loan receivable, validate risk ratings performed for criticized and classified rated borrowers with relationship exposure, value	500,000
Loan receivable, validate risk ratings performed for new regulation "O" loan commitments, value	1,000,000
Loan receivable validate risk ratings performed for leveraged loans, value	1,000,000
Loan receivable validate risk ratings performed for no borrower with commitments, value	$ 500,000
Bank modified loans and contracts | Contract	4	7	3
Post-modification outstanding recorded investment	$ 462,000	$ 6,558,000	$ 16,111,000
Loan modifications	946,300,000
Troubled debt restructurings specific reserves to customers	$ 3,000	2,800,000
Deferral [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Bank modified loans and contracts | Contract	536
Bank modified loans and contracts | Contract	54
Post-modification outstanding recorded investment	$ 73,972,000
Deferral [Member] | Loan Level Swaps [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Bank modified loans and contracts | Contract	2
Post-modification outstanding recorded investment	$ 29,300,000
Substandard [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing receivable impaired loan	16,200,000	35,900,000
Minimum [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Loan receivable, validate risk ratings performed for large sample of borrowers with relationship, value	$ 1,000,000
Minimum [Member] | Deferral [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Deferral of principal and interest periods	90 days
Maximum [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Loan receivable, validate risk ratings performed for small sample of borrowers with relationship, value	$ 1,000,000
Maximum [Member] | Deferral [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Deferral of principal and interest periods	180 days
Residential and Commercial Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Transfer of loans to loans held for sale	$ 18,500,000
Multifamily Property [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Loans held for sale, at lower of cost or fair value			$ 131,300,000
Commercial and Industrial Sector [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Loans held for sale, at lower of cost or fair value		$ 5,000,000.0
Number of loan sold | Loan		1
Paycheck Protection Program [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Loans held for sale, at lower of cost or fair value	355,000,000.0
Gain (loss) on loans held for sale at lower of cost or fair value	$ 7,400,000