Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Mortgage servicing rights [Member]
Assets:
Assets, Total	$ 2,689	$ 2,549	$ 2,747	$ 0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets, Total	50,908	66,097
Other Observable Inputs (Level 2) [Member]
Assets:
Assets, Total	234,401	202,630
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, Total	824,041	837,373
Recurring [Member]
Assets:
Assets, Total	234,680	202,795
Recurring [Member] \| U.S. Treasury [Member]
Assets:
Assets, Total	2,023	2,030
Recurring [Member] \| Government sponsored enterprises [Member]
Assets:
Assets, Total	69,576	55,180
Recurring [Member] \| Asset-backed securities [Member]
Assets:
Assets, Total	124,918	107,872
Recurring [Member] \| Obligations of states and political subdivisions [Member]
Assets:
Assets, Total	35,474	35,164
Recurring [Member] \| Mortgage servicing rights [Member]
Assets:
Assets, Total	2,689	2,549
Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets, Total	2,023	2,030
Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. Treasury [Member]
Assets:
Assets, Total	2,023	2,030
Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Government sponsored enterprises [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Asset-backed securities [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Obligations of states and political subdivisions [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Mortgage servicing rights [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Other Observable Inputs (Level 2) [Member]
Assets:
Assets, Total	229,968	198,216
Recurring [Member] \| Other Observable Inputs (Level 2) [Member] \| U.S. Treasury [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Other Observable Inputs (Level 2) [Member] \| Government sponsored enterprises [Member]
Assets:
Assets, Total	69,576	55,180
Recurring [Member] \| Other Observable Inputs (Level 2) [Member] \| Asset-backed securities [Member]
Assets:
Assets, Total	124,918	107,872
Recurring [Member] \| Other Observable Inputs (Level 2) [Member] \| Obligations of states and political subdivisions [Member]
Assets:
Assets, Total	35,474	35,164
Recurring [Member] \| Other Observable Inputs (Level 2) [Member] \| Mortgage servicing rights [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, Total	2,689	2,549
Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| U.S. Treasury [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Government sponsored enterprises [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Asset-backed securities [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Obligations of states and political subdivisions [Member]
Assets:
Assets, Total	0	0
Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Mortgage servicing rights [Member]
Assets:
Assets, Total	$ 2,689	$ 2,549