Other Comprehensive Income (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Summary of activity in accumulated other comprehensive income
Net income (loss)	$ 34,382	$ (2,779)	$ 57,235	$ (29,168)	$ (856)
Investment securities available for sale
Net unrealized gains (losses)			80,763	38,869	(38,278)
Reclassification adjustment for net (gains) realized in net income			58	(23,435)	(24,917)
Income tax (expense) benefit			(31,347)	(5,586)	24,785
Other comprehensive income (loss) on investment securities available for sale			49,474	9,848	(38,410)
Defined benefit pension and postretirement obligations:
Prior service cost, net of amortization			233	233	467
Net loss, net of amortization			903	810	2,271
Income tax expense			(441)	(566)	(1,106)
Other comprehensive income on pension and postretirement obligations			695	477	1,632
Derivatives used in cash flow hedging relationships
Net unrealized losses			(374)	(3,952)	(4,542)
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income			2,962	3,000	6,013
Income tax (expense) benefit			(1,038)	368	(499)
Other comprehensive income (loss) on cash flow hedging relationships			1,550	(584)	972
Other comprehensive income (loss)			51,719	9,741	(35,806)
Comprehensive income (loss)			$ 108,954	$ (19,427)	$ (36,662)