ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Reclassified out of AOCI) (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Amounts reclassified out of each component of accumulated other comprehensive income
Tax benefit	$ (6,810)	$ (6,067)
Net income	13,079	11,181
Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Net income	(263)	(250)
Investment Securities
Amounts reclassified out of each component of accumulated other comprehensive income
Reclassification from AOCI, net of tax	0	0
Defined Benefit Plans
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	613	(376)
Amortization of defined benefit plan items, tax	(249)	126
Reclassification from AOCI, net of tax	(263)	(250)
Defined Benefit Plans | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(429)	(376)
Amortization of defined benefit plan items, tax	166	126
Net actuarial loss
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(421)	(367)
Amortization of defined benefit plan items, tax	164	124
Reclassification from AOCI, net of tax	(257)	(243)
Net actuarial loss | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(421)	(367)
Net transition obligation
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(4)	(4)
Amortization of defined benefit plan items, tax	1	1
Reclassification from AOCI, net of tax	(3)	(3)
Net transition obligation | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(4)	(4)
Prior service cost
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	(4)	(5)
Amortization of defined benefit plan items, tax	1	1
Reclassification from AOCI, net of tax	(3)	(4)
Prior service cost | Amount Reclassified from AOCI
Amounts reclassified out of each component of accumulated other comprehensive income
Amortization of defined benefit plan items, before tax	$ (4)	$ (5)