Mortgage Banking Activities, Loan Servicing Portfolio (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Stratification of Mortgage Loan Servicing Portfolio [Line Items]
Fair value	$ 109,840,000	$ 100,812,000	$ 98,138,000	$ 86,783,000
Outstanding principal of loans serviced for others	12,272,691,000
Weighted average prepayment rate (in hundredths)	15.55%
Increase in Fair Value Of Mortgage Servicing Rights Due To 50 Basis Point Increase In Mortgage Interest Rates	2,400,000
Decrease in Fair Value Of Mortgage Servicing Rights Due To 50 Basis Point Decrease In Mortgage Interest Rates	2,000,000
Interest Rate Range Less than 4.00% [Member]
Stratification of Mortgage Loan Servicing Portfolio [Line Items]
Fair value	42,981,000
Outstanding principal of loans serviced for others	4,139,279,000
Weighted average prepayment rate (in hundredths)	8.10%
Interest Rate Range 4.00% to 4.99% [Member]
Stratification of Mortgage Loan Servicing Portfolio [Line Items]
Fair value	38,471,000
Outstanding principal of loans serviced for others	3,844,365,000
Weighted average prepayment rate (in hundredths)	10.60%
Interest Rate Range 5.00% to 5.99% [Member]
Stratification of Mortgage Loan Servicing Portfolio [Line Items]
Fair value	22,991,000
Outstanding principal of loans serviced for others	2,790,646,000
Weighted average prepayment rate (in hundredths)	19.67%
Interest Rate Range Greater than 5.99% [Member]
Stratification of Mortgage Loan Servicing Portfolio [Line Items]
Fair value	5,397,000
Outstanding principal of loans serviced for others	$ 1,498,401,000
Weighted average prepayment rate (in hundredths)	41.21%