Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 40,982	$ 39,524	$ 140,473	$ 112,602
Unrealized gains on securities:
Change in unrealized securities gains arising during period	3,470	14,783	(36,998)	16,376
Deferred tax benefit (expense)	(1,177)	(5,949)	14,657	(6,582)
Reclassification adjustment for losses (gains) included in income before income taxes	0	(31)	0	(34)
Deferred tax expense (benefit)	0	12	0	13
Total change in unrealized gains on securities, net of tax	2,293	8,815	(22,341)	9,773
Change in fair value of cash flow hedges:
Change in unrecognized loss on cash flow hedges	(544)	(919)	26	(2,750)
Deferred tax benefit (expense)	214	364	(11)	1,086
Reclassification adjustment for gains (losses) included in income before income taxes	831	769	2,463	2,294
Deferred tax benefit	(400)	(304)	(1,044)	(906)
Total change in unrecognized loss on cash flow hedges, net of tax	101	(90)	1,434	(276)
Change in pension obligation:
Reclassification adjustment for losses included in income before income taxes	4,298	2,788	12,896	8,368
Deferred tax expense	(2,061)	(1,092)	(5,428)	(3,277)
Total change in pension obligation, net of tax	2,237	1,696	7,468	5,091
Net current period other comprehensive income (loss)	4,631	10,421	(13,439)	14,588
Total comprehensive income	$ 45,613	$ 49,945	$ 127,034	$ 127,190