CHANGE IN ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ 724,345	$ 687,336
Other comprehensive (loss) income before reclassifications	$ (6,144)	$ 1,331	(23,474)	5,994
Less: Amounts reclassified from accumulated other comprehensive (loss) income	(144)	(596)	(375)	(1,500)
Net current-period other comprehensive income (loss)	(6,288)	735	(23,849)	4,494
Ending Balance	798,822	740,861	798,822	740,861
Net change in investment securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(24,186)	(4,342)	(7,842)	(8,194)
Other comprehensive (loss) income before reclassifications	(6,042)	1,289	(22,370)	5,802
Less: Amounts reclassified from accumulated other comprehensive (loss) income	0	(475)	(16)	(1,136)
Net current-period other comprehensive income (loss)	(6,042)	814	(22,386)	4,666
Ending Balance	(30,228)	(3,528)	(30,228)	(3,528)
Net change in investment securities held to maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	987	1,194	1,223	1,392
Other comprehensive (loss) income before reclassifications	0	0	0	0
Less: Amounts reclassified from accumulated other comprehensive (loss) income	(107)	(99)	(343)	(297)
Net current-period other comprehensive income (loss)	(107)	(99)	(343)	(297)
Ending Balance	880	1,095	880	1,095
Net change in defined benefit plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	894	912	865	957
Other comprehensive (loss) income before reclassifications	7	0	15	0
Less: Amounts reclassified from accumulated other comprehensive (loss) income	(37)	(22)	(16)	(67)
Net current-period other comprehensive income (loss)	(30)	(22)	(1)	(67)
Ending Balance	864	890	864	890
Net change in fair value of derivatives used for cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(3,408)	(1,622)	(2,398)	(1,772)
Other comprehensive (loss) income before reclassifications	(109)	42	(1,119)	192
Less: Amounts reclassified from accumulated other comprehensive (loss) income	0	0	0	0
Net current-period other comprehensive income (loss)	(109)	42	(1,119)	192
Ending Balance	(3,517)	(1,580)	(3,517)	(1,580)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(25,713)	(3,858)	(8,152)	(7,617)
Ending Balance	$ (32,001)	$ (3,123)	$ (32,001)	$ (3,123)