DERIVATIVES - Interest Rate Swaps Designated as Cash Flow Hedges (Details) - Interest rate swaps - Derivative designated as a cash flow hedge - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Derivatives
Notional amounts	$ 265,000	$ 290,000
Weighted average pay rates (as a percent)	1.79%	1.78%
Weighted average receive rates (as a percent)	2.36%	1.61%
Weighted average maturity	2 years 1 month 2 days	2 years 7 months 21 days