Other Comprehensive Income (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Summary of activity in accumulated other comprehensive income
Net income (loss)	$ 41,339	$ 14,304	$ 98,574	$ (14,864)	$ (856)
Investment securities available for sale
Net unrealized gains (losses)			94,907	49,929	(38,278)
Reclassification adjustment for net (gains) losses realized in net income			802	(26,800)	(24,917)
Income tax (expense) benefit			(37,119)	(8,558)	24,785
Other comprehensive income (loss) on investment securities available for sale			58,590	14,571	(38,410)
Defined benefit pension and postretirement obligations:
Prior service cost, net of amortization			349	349	467
Net loss, net of amortization			1,354	1,215	2,271
Income tax expense			(661)	(604)	(1,106)
Other comprehensive income on pension and postretirement obligations			1,042	960	1,632
Derivatives used in cash flow hedging relationships
Net unrealized losses			(528)	(4,780)	(4,542)
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income			3,969	4,512	6,013
Income tax (expense) benefit			(1,386)	103	(499)
Other comprehensive income (loss) on cash flow hedging relationships			2,055	(165)	972
Total other comprehensive income (loss)			61,687	15,366	(35,806)
Comprehensive income (loss)			$ 160,261	$ 502	$ (36,662)