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
Other Comprehensive Income [Abstract]
Net income	$ 47,888	$ 43,317	$ 95,276	$ 85,950
Investment securities available for sale:
Net unrealized gains (losses)	(111,829)	1,305	(121,760)	(609)
Reclassification adjustment for net (gains) losses realized in net income	(34)	(563)	(334)	(603)
Income tax (expense) benefit	43,188	(290)	47,138	472
Other comprehensive income (loss) on investment securities available for sale	(68,675)	452	(74,956)	(740)
Defined benefit pension and postretirement obligations:
Amortization of prior service cost	17	60	35	120
Amortization of actuarial losses	1,073	640	2,145	1,280
Income tax (expense) benefit	(421)	(273)	(842)	(546)
Other comprehensive income on pension and postretirement obligations	669	427	1,338	854
Derivatives used in cash flow hedging relationships:
Net unrealized gains (losses)	0	(24)	0	(14)
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income	0	727	0	1,458
Income tax (expense) benefit	0	(281)	0	(581)
Other comprehensive income (loss) on cash flow hedging relationships	0	422	0	863
Total other comprehensive income (loss)	(68,006)	1,301	(73,618)	977
Comprehensive income (loss)	$ (20,118)	$ 44,618	$ 21,658	$ 86,927