OTHER COMPREHENSIVE INCOME (LOSS) Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ 7,130	$ 10,860	26,060	21,759
Less: Amounts reclassified from AOCI			0	21
Other comprehensive income (loss)	7,130	10,839	26,060	21,738
Net Unrealized Losses on Cash Flow Hedges
Other comprehensive income (loss) before reclassifications	(11)	(1,203)	(912)	(2,128)
Less: Amounts reclassified from AOCI			(210)	(251)
Other comprehensive income (loss)	52	(1,046)	(702)	(1,877)
Defined Benefit Postretirement Plans
Other comprehensive income (loss) before reclassifications	138	52	275	105
Less: Amounts reclassified from AOCI			9	9
Other comprehensive income (loss)	133	48	266	96
Accumulated other comprehensive Income (Loss)
Other comprehensive income (loss) before reclassification			25,423	19,736
Less: Amounts reclassified from AOCI			(201)	(221)
Other Comprehensive Income (Loss)	7,315	9,841	25,624	19,957
Net unrealized gains on available-for-sale securities, ending balance	29,310	3,912	29,310	3,912
Net unrealized losses on cash flow hedging derivative instruments, ending balance	(6,750)	(6,314)	(6,750)	(6,314)
Net unrecognized gains on postretirement plans, ending balance	(3,204)	(2,061)	(3,204)	(2,061)
Accumulated other comprehensive (income) loss, ending balance	$ 19,356	$ (4,463)	$ 19,356	$ (4,463)