Mortgage Servicing Rights and Mortgage Servicing Activity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2012 months	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010	Dec. 31, 2011
Changes in the carrying amount of mortgage servicing rights
Balance at beginning of period	$ 21,179		$ 21,317		$ 21,317
Additions	1,394		1,308
Amortization	(1,627)		(1,086)
Balance at end of period	20,946	21,179	21,539	21,317	21,179
Valuation allowance at beginning of period	(2,193)	(3,539)	0	0	(3,539)
Recoveries	1,346		0		(3,539)
Valuation allowance at end of period	(2,193)	(3,539)	0	0	(3,539)
Mortgage servicing rights, net carrying balance	18,753		21,539		17,640
Fair value at end of period	18,869		21,943
Changes in Key economics assumptions
Prepayment speed assumption (annual CPR)	14.30%
Decrease in fair value from 10% adverse change	913
Decrease in fair value from 25% adverse change	2,177
Discount rate assumption	9.70%
Decrease in fair value from 100 basis point adverse change	555
Decrease in fair value from 200 basis point adverse change	$ 1,075
Expected weighted-average life (in months)	79.3