Mortgage Banking (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Mortgage servicing rights [Abstract]
Balance at beginning of period	$ 50,513,000	$ 51,151,000	$ 50,513,000
Origination of servicing assets		14,160,000	18,657,000
Disposals of mortgage loans sold serviced released		0	(1,772,000)
Due to market changes		(15,130,000)	(8,943,000)
Due to runoff		(6,907,000)	(7,304,000)
Balance at end of period		43,274,000	51,151,000	50,513,000
Assumed average prepayment speed		18.55
Average discount rate (in hundredths)		10.80%
Proceeds from sale of loans serviced for others	920,900,000
Reduction in Fair Value of MSR's due to sale of assets serviced	8,500,000
Payments to acquire loans receivable			53,900,000
Residential mortgage loans sold		969,400,000	1,100,000,000
Gains on sales of residential mortgage loans, before tax		12,000,000	15,300,000	20,800,000
Servicing fee income percentage of outstanding balance of underlying loans (in hundredths)			0.33%
Mortgage loan servicing representation and warranty expenses incurred		5,100,000	2,100,000
Accrual for mortgage loan servicing representation and warranty expenses		4,300,000	900,000
Mortgage loans serviced for others		$ 4,500,000,000	$ 4,300,000,000