ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components and Related Income Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME.
Unrealized holding gains (losses) on available for sale securities	$ 2,227	$ (4,319)	$ 16,247	$ (17,137)
Reclassification adjustment for losses (gains) realized in income			(201)	7,921
Income tax effect	(649)	1,256	(4,679)	2,681
Net change in unrealized gains (losses) on available for sale securities	1,578	(3,063)	11,367	(6,535)
Reclassification adjustment for amortization realized in income	128	94	385	284
Income tax effect	(37)	(27)	(113)	(82)
Net change in post-retirement obligation	91	67	272	202
Change in fair value of derivatives used for cash flow hedges	(657)	584	(5,360)	4,431
Reclassification adjustment for gains realized in income	(331)	(374)	(1,353)	(653)
Income tax effect	288	(61)	1,958	(1,099)
Net change in unrealized (losses) gains on cash flow hedges	(700)	149	(4,755)	2,679
Other comprehensive income (loss)	$ 969	$ (2,847)	$ 6,884	$ (3,654)