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
Other Comprehensive Income [Abstract]
Net income	$ 45,658	$ 46,395	$ 140,934	$ 132,345
Investment securities available for sale:
Net unrealized gains (losses)	(20,558)	3,479	(142,318)	2,870
Reclassification adjustment for net (gains) losses realized in net income	(248)	(3,506)	(582)	(4,109)
Income tax (expense) benefit	8,031	11	55,169	483
Other comprehensive income (loss) on investment securities available for sale	(12,775)	(16)	(87,731)	(756)
Defined benefit pension and postretirement obligations:
Amortization of prior service cost	17	60	52	180
Amortization of actuarial losses	1,073	640	3,218	1,920
Income tax (expense) benefit	(420)	(273)	(1,262)	(819)
Other comprehensive income on pension and postretirement obligations	670	427	2,008	1,281
Derivatives used in cash flow hedging relationships:
Net unrealized gains (losses)	0	20	0	6
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income	0	496	0	1,954
Income tax (expense) benefit	0	(203)	0	(784)
Other comprehensive income (loss) on cash flow hedging relationships	0	313	0	1,176
Total other comprehensive income (loss)	(12,105)	724	(85,723)	1,701
Comprehensive income (loss)	$ 33,553	$ 47,119	$ 55,211	$ 134,046