Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Net carrying value of intangible assets
Goodwill	$ 113,414		$ 113,414	$ 113,414
Other intangible assets:
Total other intangible assets	10,243		11,472	11,849
Core deposit intangible assets [Member]
Other intangible assets:
Total other intangible assets	6,777		7,879	8,261
Mortgage servicing rights [Member]
Other intangible assets:
Total other intangible assets	3,466	3,463	3,593	3,561	3,577	3,782
Non-compete agreements [Member]
Other intangible assets:
Total other intangible assets	$ 0		$ 0	$ 27