CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension and other post retirement obligations:
Amortization of actuarial (losses)/gains included in net periodic pension cost, gross	$ (12,647)	$ (707)	$ 5,514
Tax effect	3,087	263	(2,108)
Amortization of actuarial (losses)/gains included in net periodic pension cost, net	(9,560)	(444)	3,406
Amortization of prior service cost included in net periodic pension cost, gross	(1,398)	(859)	(136)
Tax effect	340	324	52
Amortization of prior service cost included in net periodic pension cost, net	(1,058)	(535)	(84)
Initial projected benefit obligation recognized upon plan adoption, gross	(775)	0	0
Tax effect	189	0	0
Initial projected benefit obligation recognized upon plan adoption, net	(586)	0	0
Unamortized actuarial gain due to plan merger, gross	0	1,858	0
Tax effect	0	(711)	0
Unamortized actuarial gain due to plan merger, net	0	1,147	0
Other comprehensive (loss)/income related to pension and other post retirement obligations, net of taxes	(11,204)	168	3,322
Unrealized (losses)/gains on securities:
Net unrealized holding (losses) arising during period, gross	(39,894)	(17,851)	(24,042)
Tax effect	9,700	6,787	9,328
Net unrealized holding losses arising during period, net	(30,194)	(11,064)	(14,714)
Reclassification of other comprehensive income due to change in accounting principle - equity securities	(208)	0	0
Reclassification adjustment for net (gains) included in net income, gross	0	(2)	0
Tax effect	0	1	0
Reclassification adjustment for net gains included in net income, net	0	(1)	0
Other comprehensive (loss) related to unrealized (losses)/gains on available-for-sale securities, net of taxes	(30,402)	(11,065)	(14,714)
Other comprehensive (loss), net of tax	(41,606)	(10,897)	(11,392)
Net income	168,641	150,717	103,812
Comprehensive income	127,035	139,820	92,420
Accumulated Other Comprehensive Income/(Loss) By Component:
Unrealized (loss) for pension and other postretirement obligations	(43,497)	(28,677)	(28,969)
Tax effect	10,660	7,044	11,008
Net unrealized (loss) for pension and other postretirement obligations	(32,837)	(21,633)	(17,961)
Unrealized (loss) gain on available-for-sale securities	(16,229)	23,940	41,793
Tax effect	3,969	(6,006)	(15,989)
Reclassification of other comprehensive income due to change in accounting principle - equity securities	(208)	0	0
Net unrealized (loss) gain on available-for-sale securities	(12,468)	17,934	25,804
Accumulated other comprehensive (loss)/income	$ (45,305)	$ (3,699)	$ 7,843