Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 26,550	$ 43,906	$ 48,916	$ 99,491
Unrealized gains and losses on securities:
Change in unrealized securities gains (losses) arising during period	31,550	(38,992)	43,449	(40,468)
Tax effect	(12,225)	15,269	(16,868)	15,834
Total change in unrealized gains and losses on securities, net of tax	19,325	(23,723)	26,581	(24,634)
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	568	1,388	1,287	2,202
Tax effect	(218)	(548)	(496)	(869)
Total change in unrecognized loss on cash flow hedges, net of tax	350	840	791	1,333
Change in pension obligation:
Reclassification adjustment for gains included in income before income taxes	1,598	4,294	3,197	8,598
Tax effect	(622)	(1,682)	(1,244)	(3,367)
Total change in pension obligation, net of tax	976	2,612	1,953	5,231
Net current period other comprehensive income	20,651	(20,271)	29,325	(18,070)
Total comprehensive income	$ 47,201	$ 23,635	$ 78,241	$ 81,421