Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 55,958	$ 26,501	$ 167,638	$ 75,666
Unrealized gains and losses on securities:
Change in unrealized securities gains (losses) arising during period	28,231	(11,444)	29,420	32,006
Tax effect	(10,737)	4,444	(11,198)	(12,425)
Reclassification adjustment for net gains realized and included in income before income taxes	5,564	0	10,837	0
Tax effect	2,094	0	4,145	0
Total change in unrealized gains and losses on securities, net of tax	14,024	(7,000)	11,530	19,581
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	721	949	2,006	2,236
Tax effect	(300)	(367)	(796)	(863)
Total change in unrecognized loss on cash flow hedges, net of tax	421	582	1,210	1,373
Change in pension obligation:
Reclassification adjustment for losses included in income before income taxes	2,916	822	8,689	4,019
Tax effect	(1,078)	(319)	(3,324)	(1,563)
Total change in pension obligation, net of tax	1,838	503	5,365	2,456
Net current period other comprehensive income	16,283	(5,915)	18,105	23,410
Total comprehensive income	$ 72,241	$ 20,586	$ 185,743	$ 99,076