DERIVATIVES - Interest Rate Swaps Designated as Cash Flow Hedges (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Derivatives
Notional amounts	$ 1,100,000	$ 823,900
Interest rate swaps | Derivative designated as a cash flow hedge
Derivatives
Notional amounts	$ 280,000	$ 290,000
Weighted average pay rates (as a percent)	1.33%	1.84%
Weighted average receive rates (as a percent)	0.26%	1.94%
Weighted average maturity	3 years 4 months 20 days	2 years 10 months 28 days