Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Comprehensive Income [Abstract]
Net income (loss)	$ 178,973	$ 139,699	$ (856)
Investment securities available for sale
Net unrealized gains (losses)	(19,042)	71,606	(38,278)
Reclassification adjustment for net (gains) losses realized in net income	(4,261)	1,112	(24,917)
Income tax (expense) benefit	9,651	(28,566)	24,785
Other comprehensive income (loss) on investment securities available for sale	(13,652)	44,152	(38,410)
Defined benefit pension and postretirement obligations:
Prior service cost, net of amortization	242	467	467
Net gain (loss), net of amortization	(6,941)	(14,810)	2,271
Income tax (expense) benefit	2,366	5,674	(1,106)
Other comprehensive income (loss) on pension and postretirement obligations	(4,333)	(8,669)	1,632
Derivatives used in cash flow hedging relationships
Net unrealized gains (losses)	6	(557)	(4,542)
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income (loss)	1,954	4,708	6,013
Income tax expense	(974)	(1,658)	(499)
Other comprehensive income on cash flow hedging relationships	986	2,493	972
Total other comprehensive income (loss)	(16,999)	37,976	(35,806)
Comprehensive income (loss)	$ 161,974	$ 177,675	$ (36,662)