DERIVATIVES - Interest Rate Swaps Designated as Cash Flow Hedges (Details) - Interest rate swaps - Derivative designated as a cash flow hedge - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivatives
Notional amounts	$ 315,000	$ 240,000
Weighted average pay rates (as a percent)	1.84%	1.84%
Weighted average receive rates (as a percent)	2.61%	2.77%
Weighted average maturity	2 years 4 months 13 days	2 years 11 days