Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 M
Credit Commitments
Total Credit Commitments	2,067,895,000
Unfunded Commitments to Extend Credit
Credit Commitments
Total Credit Commitments	1,975,327,000
Standby Letters of Credit
Credit Commitments
Total Credit Commitments	74,082,000
Assets secured for standby letters of credit	36,200,000
Standby Letters of Credit | Minimum
Credit Commitments
Standby and commercial letters of credit, remaining term (in months)	1
Standby Letters of Credit | Maximum
Credit Commitments
Standby and commercial letters of credit, remaining term (in months)	27
Commercial Letters of Credit
Credit Commitments
Total Credit Commitments	18,486,000
Commercial Letters of Credit | Minimum
Credit Commitments
Standby and commercial letters of credit, remaining term (in months)	1
Commercial Letters of Credit | Maximum
Credit Commitments
Standby and commercial letters of credit, remaining term (in months)	27