Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 210,386	$ 138,562	$ 166,869
Unrealized gains (losses) on securities:
Change in unrealized securities gains (losses) arising during period	(22,030)	54,071	(50,441)
Tax effect	8,486	(21,010)	19,833
Reclassification adjustment for net gains realized and included in income before income taxes	(10,817)	(29,096)	0
Tax effect	4,138	11,224	0
Total change in unrealized gains (losses) on securities, net of tax	(20,223)	15,189	(30,608)
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	2,908	2,883	3,178
Tax effect	(1,136)	(1,113)	(1,320)
Total change in unrecognized loss on cash flow hedges, net of tax	1,772	1,770	1,858
Change in pension obligation:
Change in pension obligation	691	(78,472)	123,557
Tax effect	(297)	30,526	(48,475)
Amortization of actuarial losses and prior service cost	11,586	5,358	17,195
Tax effect	(4,988)	(2,084)	(6,689)
Total change in pension obligation, net of tax	6,992	(44,672)	85,588
Net current period other comprehensive (loss) income	(11,459)	(27,713)	56,838
Total comprehensive income	$ 198,927	$ 110,849	$ 223,707