Intangible Assets (Net Carrying Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Net carrying value of intangible assets
Goodwill	$ 120,164	$ 120,164	$ 113,414
Other intangible assets:
Total other intangible assets	14,902	15,388	10,939
Core deposit intangible assets [Member]
Other intangible assets:
Total other intangible assets	11,417	11,910	7,512
Mortgage servicing rights [Member]
Other intangible assets:
Total other intangible assets	$ 3,485	$ 3,478	$ 3,427	$ 3,593