Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 43,906	$ 37,583	$ 99,491	$ 73,078
Unrealized gains on securities:
Change in unrealized securities gains arising during period	(38,992)	4,491	(40,468)	1,593
Deferred tax benefit (expense)	15,269	(1,756)	15,834	(633)
Reclassification adjustment for losses (gains) included in income before income taxes	0	(3)	0	(3)
Deferred tax expense (benefit)	0	1	0	1
Total change in unrealized gains on securities, net of tax	(23,723)	2,733	(24,634)	958
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	569	(1,473)	570	(1,831)
Deferred tax benefit (expense)	(225)	582	(225)	722
Reclassification adjustment for gains (losses) included in income before income taxes	819	776	1,632	1,525
Deferred tax benefit	(323)	(306)	(644)	(602)
Total change in unrecognized loss on cash flow hedges, net of tax	840	(421)	1,333	(186)
Change in pension obligation:
Reclassification adjustment for losses included in income before income taxes	4,294	2,790	8,598	5,580
Deferred tax expense	(1,682)	(1,093)	(3,367)	(2,185)
Total change in pension obligation, net of tax	2,612	1,697	5,231	3,395
Net current period other comprehensive income (loss)	(20,271)	4,009	(18,070)	4,167
Total comprehensive income	$ 23,635	$ 41,592	$ 81,421	$ 77,245