ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components and Related Income Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME.
Unrealized holding gains (losses) on available for sale securities	$ 8,489	$ (4,231)	$ 14,020	$ (12,818)
Reclassification adjustment for losses (gains) realized in income	(201)	7,921	(201)	7,921
Income tax effect	(2,417)	(1,074)	(4,030)	1,425
Net change in unrealized gains (losses) on available for sale securities	5,871	2,616	9,789	(3,472)
Reclassification adjustment for amortization realized in income	129	95	257	190
Income tax effect	(38)	(27)	(76)	(55)
Net change in post-retirement obligation	91	68	181	135
Change in fair value of derivatives used for cash flow hedges	(3,106)	1,020	(4,703)	3,847
Reclassification adjustment for gains realized in income	(466)	(344)	(1,022)	(279)
Income tax effect	1,042	(197)	1,670	(1,038)
Net change in unrealized (losses) gains on cash flow hedges	(2,530)	479	(4,055)	2,530
Other comprehensive income (loss)	$ 3,432	$ 3,163	$ 5,915	$ (807)

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