CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension and other post retirement obligations:
Amortization of actuarial (gains)/losses included in net periodic pension cost, gross	$ (707)	$ 5,514	$ (7,236)
Tax effect	263	(2,108)	2,774
Amortization of actuarial (gains)/losses included in net periodic pension cost, net	(444)	3,406	(4,462)
Amortization of prior service cost included in net periodic pension cost, gross	(859)	(136)	(170)
Tax effect	324	52	65
Amortization of prior service cost included in net periodic pension cost, net	(535)	(84)	(105)
Unamortized actuarial gain due to plan merger, gross	1,858	0	0
Tax effect	(711)	0	0
Unamortized actuarial gain due to plan merger, net	1,147	0	0
Other comprehensive income/(loss) related to pension and other post retirement obligations, net of taxes	168	3,322	(4,567)
Unrealized (losses)/gains on securities:
Net unrealized holding losses arising during period, gross	(17,851)	(24,042)	(9,209)
Tax effect	6,787	9,328	2,289
Net unrealized holding losses arising during period, net	(11,064)	(14,714)	(6,920)
Reclassification adjustment for net (gains)/losses included in net income, gross	(2)	0	4
Tax effect	1	0	(2)
Reclassification adjustment for net gains/losses included in net income, net	(1)	0	2
Other comprehensive (loss) related to unrealized (losses)/gains on available-for-sale securities, net of taxes	(11,065)	(14,714)	(6,918)
Other comprehensive (loss), net of tax	(10,897)	(11,392)	(11,485)
Net income	150,717	103,812	91,230
Comprehensive income	139,820	92,420	79,745
Accumulated Other Comprehensive Income/(Loss) By Component:
Unrealized loss for pension and other postretirement obligations	(28,677)	(28,969)	(34,347)
Tax effect	7,044	11,008	13,064
Net unrealized loss for pension and other postretirement obligations	(21,633)	(17,961)	(21,283)
Unrealized gain on available-for-sale securities	23,940	41,793	65,835
Tax effect	(6,006)	(15,989)	(25,317)
Net unrealized gain on available-for-sale securities	17,934	25,804	40,518
Accumulated other comprehensive (loss)/income	$ (3,699)	$ 7,843	$ 19,235