Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 225,482	$ 210,386	$ 138,562
Unrealized (losses) gains on securities:
Change in unrealized securities (losses) gains arising during period	(21,530)	(22,030)	54,071
Tax effect	7,584	8,486	(21,010)
Reclassification adjustment for net gains realized and included in income before income taxes	(26,673)	(10,817)	(29,096)
Tax effect	9,869	4,138	11,224
Total change in unrealized (losses) gains on securities, net of tax	(30,750)	(20,223)	15,189
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	1,429	2,908	2,883
Tax effect	(537)	(1,136)	(1,113)
Total change in unrecognized loss on cash flow hedges, net of tax	892	1,772	1,770
Change in pension obligation:
Change in pension obligation	(70,424)	691	(78,472)
Tax effect	25,077	(297)	30,526
Amortization of actuarial losses and prior service cost	7,069	11,586	5,358
Tax effect	(2,616)	(4,988)	(2,084)
Total change in pension obligation, net of tax	(40,894)	6,992	(44,672)
Net current period other comprehensive (loss) income	(70,752)	(11,459)	(27,713)
Total comprehensive income	$ 154,730	$ 198,927	$ 110,849