Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 138,562	$ 166,869	$ 132,395
Change in unrealized gains and losses on securities:
Change in unrealized securities gains (losses) arising during period	(4,121)	(50,441)	9,566
Tax effect	1,438	19,833	(3,759)
Reclassification adjustment for gains included in income before income taxes	29,096	0	(2,322)
Tax effect	(11,224)	0	917
Total change in unrealized gains (losses) on securities, net of tax	15,189	(30,608)	4,402
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	2,883	3,178	316
Tax effect	(1,113)	(1,320)	(125)
Total change in unrecognized loss on cash flow hedges, net of tax	1,770	1,858	191
Change in pension obligation:
Change in pension obligation	(78,472)	123,557	(44,315)
Tax effect	30,526	(48,475)	17,354
Reclassification adjustment for gains included in income before income taxes	5,358	17,195	11,236
Tax effect	(2,084)	(6,689)	(4,400)
Total change in pension obligation, net of tax	(44,672)	85,588	(20,125)
Net current period other comprehensive income (loss)	(27,713)	56,838	(15,532)
Total comprehensive income	$ 110,849	$ 223,707	$ 116,863