SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash flow reporting (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Reserve required at federal reserve bank	$ 16,200		$ 18,600
Cash collateral used in interest rate swap transactions	10,100		$ 3,100
Supplemental disclosures of cash flow information:
Cash paid for taxes	3,707	$ 4,323
Cash paid for interest	6,444	7,789
Supplemental disclosures of non-cash flow information:
Operating lease right-to-use asset obtained in exchange for lease liabilities	1,898	13,208
Dividends accrued	$ (6)	1,292
Repossessed real estate and other assets		$ 77