ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Components and Related Income Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)
Unrealized holding gains (losses) on available for sale securities	$ 9,069	$ 15,524	$ (8,429)
Reclassification adjustments for (gains) losses realized in income	(3,525)	(201)	7,921
Income tax effect	(1,628)	(4,467)	160
Net change in unrealized (losses) gains on available for sale securities	3,916	10,856	(348)
Unrealized net losses arising during the period	3,245	1,076	1,567
Reclassification adjustments for amortization realized in income	581	487	384
Income tax effect	799	179	351
Net change in post-retirement obligation	(1,865)	(410)	(832)
Change in fair value of derivatives used for cash flow hedges	(10,455)	(3,601)	2,493
Reclassification adjustments for losses (gains) realized in income	5,016	(1,588)	(1,068)
Income tax effect	1,601	1,514	(418)
Net change in unrealized (losses) gains on cash flow hedges	(3,838)	(3,675)	1,007
Other comprehensive income (loss)	$ (1,787)	$ 6,771	$ (173)