DERIVATIVES - Interest Rate Swaps Designated as Cash Flow Hedges (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivatives
Notional amounts	$ 918,800	$ 823,900
Interest rate swaps | Derivative designated as a cash flow hedge
Derivatives
Notional amounts	$ 305,000	$ 290,000
Weighted average pay rates (as a percent)	1.84%	1.84%
Weighted average receive rates (as a percent)	1.38%	1.94%
Weighted average maturity	4 years 1 month 6 days	2 years 10 months 28 days