CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension and other post retirement obligations:
Amortization of actuarial losses included in net periodic pension cost, gross	$ (2,563)	$ (12,647)	$ (707)
Tax effect	605	3,087	263
Amortization of actuarial losses included in net periodic pension cost, net	(1,958)	(9,560)	(444)
Amortization of prior service cost included in net periodic pension cost, gross	(115)	(1,398)	(859)
Tax effect	28	340	324
Amortization of prior service cost included in net periodic pension cost, net	(87)	(1,058)	(535)
Initial projected benefit obligation recognized upon plan adoption, gross	0	(775)	0
Tax effect	0	189	0
Initial projected benefit obligation recognized upon plan adoption, net	0	(586)	0
Unamortized actuarial gain due to plan merger, gross	0	0	1,858
Tax effect	0	0	(711)
Unamortized actuarial gain due to plan merger, net	0	0	1,147
Other comprehensive (loss)/income related to pension and other post retirement obligations, net of taxes	(2,045)	(11,204)	168
Unrealized gains/(losses) on available-for-sale securities:
Net unrealized holding gains (losses) arising during period, gross	53,988	(39,894)	(17,851)
Tax effect	(13,176)	9,700	6,787
Net unrealized holding gains (losses) arising during period, net	40,812	(30,194)	(11,064)
Reclassification of other comprehensive income due to change in accounting principle - equity securities	0	(208)	0
Reclassification adjustment for net (gains) included in net income, gross	(4,882)	0	(2)
Tax effect	1,194	0	1
Reclassification adjustment for net (gains) included in net income, net	(3,688)	0	(1)
Other comprehensive gain (loss) related to unrealized gains/(losses) on available-for-sale securities, net of taxes	37,124	(30,402)	(11,065)
Other comprehensive income (loss), net of tax	35,079	(41,606)	(10,897)
Net income	169,063	168,641	150,717
Comprehensive income	204,142	127,035	139,820
Accumulated Other Comprehensive Income/(Loss) By Component:
Unrealized (loss) for pension and other postretirement obligations	(46,175)	(43,497)	(28,677)
Tax effect	11,293	10,660	7,044
Net unrealized (loss) for pension and other postretirement obligations	(34,882)	(32,837)	(21,633)
Unrealized gain (loss) on available-for-sale securities	32,877	(16,229)	23,940
Tax effect	(8,221)	3,761	(6,006)
Net unrealized gain (loss) on available-for-sale securities	24,656	(12,468)	17,934
Accumulated other comprehensive (loss)	$ (10,226)	$ (45,305)	$ (3,699)