Mortgage Servicing Rights and Mortgage Servicing Activity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2012 months	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2011
Transfers and Servicing [Abstract]
Balance at beginning of period	$ 21,273	$ 20,781			$ 21,179	$ 21,317	$ 21,317		$ 21,094
Additions	1,408		798		4,597	2,660
Amortization	(1,390)		(1,111)		(4,485)	(3,196)
Balance at end of period	21,291	21,179	20,781	21,317	21,291	20,781	21,179	21,317	21,094
Valuation allowance at beginning of period	(4,078)	(3,488)	(3,989)	(350)			(3,539)	0
Recoveries	(590)		(3,639)		(539)	(3,989)	(3,500)
Valuation allowance at end of period	(4,078)	(3,488)	(3,989)	(350)			(3,539)	0
MSR Net Carrying Amount	17,213	17,600	16,792		17,213	16,792	17,600
Fair value at end of period	17,294				17,294				16,866
Changes in Key economics assumptions
Prepayment speed assumption (annual CPR)	17.50%
Decrease in fair value from 10% adverse change	921				921
Decrease in fair value from 25% adverse change	2,193				2,193
Discount rate assumption	9.70%
Decrease in fair value from 100 basis point adverse change	478				478
Decrease in fair value from 200 basis point adverse change	$ 926				$ 926
Expected weighted-average life (in months)	71.5