Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Net carrying value of intangible assets
Goodwill	$ 113,414		$ 113,414	$ 113,414
Other intangible assets:
Total other intangible assets	10,607		11,472	12,327
Core deposit intangible assets [Member]
Other intangible assets:
Total other intangible assets	7,144		7,879	8,643
Mortgage servicing rights [Member]
Other intangible assets:
Total other intangible assets	3,463	3,427	3,593	3,577	3,832	3,782
Non-compete agreements [Member]
Other intangible assets:
Total other intangible assets				$ 107