ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), Before and After Tax Amounts by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Change in unrealized holding loss on securities held-to-maturity and transferred securities [Abstract]
Accretion of previously recognized non-credit component of OTTI	$ 0	$ 9
Change in unrealized loss on securities transferred to held-to-maturity	0	25
Net change	0	34
Tax expense	0	16
Net change in unrealized holding loss on securities held-to-maturity and transferred securities	0	18
Change in unrealized holding gain on securities available-for-sale [Abstract]
Change in net unrealized gain during the period	(1,188)	120
Reclassification adjustment for net gains included in net gain on securities and other assets	(1,370)	0
Net change	(2,558)	120
Tax expense (benefit)	(850)	55
Net change in unrealized holding gain on securities available-for-sale	(1,708)	65
Change in pension and other postretirement obligations [Abstract]
Reclassification adjustment for expense included in salaries and employee benefits expense	286	0
Change in the net actuarial gain or loss	(131)	302
Net change	155	302
Tax expense	51	131
Net change in pension and other postretirement obligations	104	171
Change in unrealized loss on derivatives asset or liability [Abstract]
Change in net unrealized loss during the period	2,081	228
Reclassification adjustment for expense included in interest expense	(65)	87
Net change	2,016	315
Tax expense	687	144
Net change in unrealized loss on derivatives asset or liability	1,329	171
Other comprehensive income (loss), net of tax	$ (275)	$ 425