ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components and Related Income Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME.
Unrealized holding gains (losses) on available for sale securities	$ 5,531	$ (8,587)
Income tax effect	(1,613)	2,499
Net change in unrealized gains (losses) on available for sale securities	3,918	(6,088)
Reclassification adjustment for amortization realized in income	128	95
Income tax effect	(38)	(28)
Net change in post-retirement obligation	90	67
Change in fair value of derivatives used for cash flow hedges	(1,597)	2,827
Reclassification adjustment for (gains) losses realized in income	(556)	65
Income tax effect	628	(841)
Net change in unrealized (losses) gains on cash flow hedges	(1,525)	2,051
Other comprehensive income (loss)	$ 2,483	$ (3,970)

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