OTHER COMPREHENSIVE INCOME (LOSS) Accumulated Other Comprehensive Income (Loss) (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 Income (Loss) [Roll Forward]
Net unrealized gains on available-for-sale securities, beginning balance			$ 3,250	$ (17,826)
Net unrealized losses on cash flow hedging derivative instruments, beginning balance			(6,048)	(4,437)
Net unrecognized gains on postretirement plans, beginning balance			(3,470)	(2,157)
Accumulated other comprehensive (income) loss, beginning balance			(6,268)	(24,420)
Net Unrealized Gains (Losses) on AFS Securities
Other comprehensive income (loss) before reclassifications	$ (586)	$ 3,573	25,474	25,332
Less: Amounts reclassified from AOCI			0	22
Other comprehensive income (loss)	(586)	3,572	25,474	25,310
Net Unrealized Losses on Cash Flow Hedges
Other comprehensive income (loss) before reclassifications	540	(310)	(328)	(2,438)
Less: Amounts reclassified from AOCI			(298)	(520)
Other comprehensive income (loss)	672	(41)	(30)	(1,918)
Defined Benefit Postretirement Plans
Other comprehensive income (loss) before reclassifications	138	54	413	159
Less: Amounts reclassified from AOCI			14	14
Other comprehensive income (loss)	133	49	399	145
Accumulated other comprehensive Income (Loss)
Other comprehensive income (loss) before reclassification			25,559	23,053
Less: Amounts reclassified from AOCI			(284)	(484)
Other Comprehensive Income (Loss)	219	3,580	25,843	23,537
Net unrealized gains on available-for-sale securities, ending balance	28,724	7,484	28,724	7,484
Net unrealized losses on cash flow hedging derivative instruments, ending balance	(6,078)	(6,355)	(6,078)	(6,355)
Net unrecognized gains on postretirement plans, ending balance	(3,071)	(2,012)	(3,071)	(2,012)
Accumulated other comprehensive (income) loss, ending balance	$ 19,575	$ (883)	$ 19,575	$ (883)