Mortgage Servicing Rights and Mortgage Servicing Activity (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 months	Dec. 31, 2010	Dec. 31, 2009
Changes in the carrying amount of mortgage servicing rights
Balance at beginning of period	$ 21,317	$ 20,784	$ 18,778
Addition of mortgage servicing rights	4,442	4,966	4,862
Amortization	(4,580)	(4,433)	(3,641)
Changes in allowance for impairment	(3,539)	0	785
Balance at end of period	17,640	21,317	20,784
Fair value at end of period	17,749	21,579	22,241
Changes in Key economics assumptions
Prepayment speed assumption (annual CPR)	15.90%
Decrease in fair value from 10% adverse change	908
Decrease in fair value from 25% adverse change	2,152
Discount rate assumption	9.70%
Decrease in fair value from 100 basis point adverse change	500
Decrease in fair value from 200 basis point adverse change	$ 969
Expected weighted-average life (in months)	74.1