Consolidated Statement of Other Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Other Comprehensive Income [Abstract]
Net income	$ 46,395	$ 41,339	$ 132,345	$ 98,574
Investment securities available for sale:
Net unrealized gains (losses)	3,479	14,144	2,870	94,907
Reclassification adjustment for net (gains) losses realized in net income	(3,506)	744	(4,109)	802
Income tax (expense) benefit	11	(5,772)	483	(37,119)
Other comprehensive income (loss) on investment securities available for sale	(16)	9,116	(756)	58,590
Defined benefit pension and postretirement obligations:
Prior service cost, net of amortization	60	116	180	349
Net loss, net of amortization	640	451	1,920	1,354
Income tax expense	(273)	(220)	(819)	(661)
Other comprehensive income on pension and postretirement obligations	427	347	1,281	1,042
Derivatives used in cash flow hedging relationships:
Net unrealized gains (losses)	20	(154)	6	(528)
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income	496	1,007	1,954	3,969
Income tax expense	(203)	(348)	(784)	(1,386)
Other comprehensive income on cash flow hedging relationships	313	505	1,176	2,055
Total other comprehensive income	724	9,968	1,701	61,687
Comprehensive income	$ 47,119	$ 51,307	$ 134,046	$ 160,261