Mortgage Servicing Rights and Mortgage Servicing Activity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2012 months	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2011
Transfers and Servicing [Abstract]
Balance at beginning of period	$ 20,946		$ 21,539		$ 21,179	$ 21,317	$ 21,317
Additions	1,794		554		3,188	1,862
Amortization	(1,467)		(999)		(3,094)	(2,085)
Balance at end of period	21,273	21,179	21,094	21,317	21,273	21,094	21,179	21,317
Valuation allowance at beginning of period	(3,488)	(2,193)	(350)	0			(3,539)	0
Recoveries	(1,295)		(350)		51	(350)	(3,539)
Valuation allowance at end of period	(3,488)	(2,193)	(350)	0			(3,539)	0
MSR Net Carrying Amount	17,785	17,640	20,744		17,785	20,744	17,640
Fair value at end of period	17,913				17,913				20,766
Changes in Key economics assumptions
Prepayment speed assumption (annual CPR)	16.90%
Decrease in fair value from 10% adverse change	945				945
Decrease in fair value from 25% adverse change	2,238				2,238
Discount rate assumption	9.70%
Decrease in fair value from 100 basis point adverse change	498				498
Decrease in fair value from 200 basis point adverse change	$ 965				$ 965
Expected weighted-average life (in months)	71.3