ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components and Related Income Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME
Unrealized holding (losses) gains on available for sale securities	$ (935)	$ 2,227	$ 9,186	$ 16,247
Reclassification adjustments for gains realized in income	(3,540)		(3,525)	(201)
Income tax effect	1,309	(649)	(1,655)	(4,679)
Net change in unrealized (losses) gains on available for sale securities	(3,166)	1,578	4,006	11,367
Reclassification adjustments for amortization realized in income	136	128	412	385
Income tax effect	(39)	(37)	(120)	(113)
Net change in post-retirement obligation	97	91	292	272
Change in fair value of derivatives used for cash flow hedges	3,364	(657)	(7,709)	(5,360)
Reclassification adjustments for losses (gains) realized in income	992	(331)	1,058	(1,353)
Income tax effect	(1,274)	288	1,945	1,958
Net change in unrealized gains (losses) on cash flow hedges	3,082	(700)	(4,706)	(4,755)
Other comprehensive income (loss)	$ 13	$ 969	$ (408)	$ 6,884

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