Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 69,316	$ 44,522	$ 121,388	$ 111,680
Unrealized gains and losses on securities:
Change in unrealized securities gains (losses) arising during period	24,176	(29,226)	92,209	1,189
Tax effect	(9,261)	11,352	(35,277)	(461)
Reclassification adjustment for net gains realized and included in income before income taxes	(12,529)	(147)	(17,157)	(5,273)
Tax effect	4,793	74	6,563	2,051
Total change in unrealized gains and losses on securities, net of tax	7,179	(17,947)	46,338	(2,494)
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	729	709	1,429	1,285
Tax effect	(274)	(274)	(537)	(496)
Total change in unrecognized loss on cash flow hedges, net of tax	455	435	892	789
Change in pension obligation:
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	1,882	2,887	3,534	5,773
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax	(719)	(1,123)	(1,351)	(2,246)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	1,163	1,764	2,183	3,527
Net current period other comprehensive income	8,797	(15,748)	49,413	1,822
Total comprehensive income	$ 78,113	$ 28,774	$ 170,801	$ 113,502