ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Components of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in each component of AOCI, net of tax
Balance at beginning of period			$ 504,675	$ 494,639
Total other comprehensive income (loss), net of tax	$ (8)	$ (1,793)	4,737	16,425
Balance at end of period	509,870	519,492	509,870	519,492
Investment Securities
Changes in each component of AOCI, net of tax
Balance at beginning of period	9,648	26,900	4,729	9,181
Other comprehensive income/loss before reclassifications	(293)	(2,042)	3,639	15,677
Amounts reclassified from AOCI	0	0	987	0
Total other comprehensive income (loss), net of tax	(293)	(2,042)	4,626	15,677
Balance at end of period	9,355	24,858	9,355	24,858
Defined Benefit Plans
Changes in each component of AOCI, net of tax
Balance at beginning of period	(6,424)	(8,479)	(6,250)	(8,978)
Other comprehensive income/loss before reclassifications	0	0	(627)	0
Amounts reclassified from AOCI	285	249	738	748
Total other comprehensive income (loss), net of tax	285	249	111	748
Balance at end of period	(6,139)	(8,230)	(6,139)	(8,230)
Accumulated Other Comprehensive Income
Changes in each component of AOCI, net of tax
Balance at beginning of period	3,224	18,421	(1,521)	203
Other comprehensive income/loss before reclassifications	(293)	(2,042)	3,012	15,677
Amounts reclassified from AOCI	285	249	1,725	748
Total other comprehensive income (loss), net of tax	(8)	(1,793)	4,737	16,425
Balance at end of period	$ 3,216	$ 16,628	$ 3,216	$ 16,628