ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components and Related Income Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS).
Unrealized holding gains (losses) on available for sale securities	$ 15,524	$ (8,429)	$ (1,107)
Reclassification adjustments for (gains) losses realized in income	(201)	7,921	(38)
Income tax effect	(4,467)	160	640
Net change in unrealized gains (losses) on available for sale securities	10,856	(348)	(505)
Unrealized net loss arising during the period	1,076	1,567	302
Reclassification adjustments for amortization realized in income	487	384	480
Income tax effect	179	351	15
Net change in post-retirement obligation	(410)	(832)	193
Change in fair value of derivatives used for cash flow hedges	(3,601)	2,493	463
Reclassification adjustments for (gains) losses realized in income	(1,588)	(1,068)	1,419
Income tax effect	1,514	(418)	(793)
Net change in unrealized (losses) gains on cash flow hedges	(3,675)	1,007	1,089
Other comprehensive income (loss)	$ 6,771	$ (173)	$ 777

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