Fair Value Measurements - Financial Instruments Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																																			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Obligations of U.S. Government sponsored enterprises	Dec. 31, 2012 Obligations of U.S. Government sponsored enterprises	Mar. 31, 2013 Obligations of states and political subdivisions	Dec. 31, 2012 Obligations of states and political subdivisions	Mar. 31, 2013 Residential mortgage-backed securities	Dec. 31, 2012 Residential mortgage-backed securities	Mar. 31, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1)	Dec. 31, 2012 Quoted Prices in Active Markets for Identical Assets (Level 1)	Mar. 31, 2013 Significant Other Observable Inputs (Level 2)	Dec. 31, 2012 Significant Other Observable Inputs (Level 2)	Mar. 31, 2013 Significant Unobservable Inputs (Level 3)	Dec. 31, 2012 Significant Unobservable Inputs (Level 3)	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) Auction Rate Securities security	Mar. 31, 2013 Total Fair Value	Dec. 31, 2012 Total Fair Value	Mar. 31, 2013 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1)	Mar. 31, 2013 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1) Obligations of U.S. Government sponsored enterprises	Mar. 31, 2013 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1) Obligations of states and political subdivisions	Mar. 31, 2013 Recurring basis Quoted Prices in Active Markets for Identical Assets (Level 1) Residential mortgage-backed securities	Mar. 31, 2013 Recurring basis Significant Other Observable Inputs (Level 2)	Mar. 31, 2013 Recurring basis Significant Other Observable Inputs (Level 2) Obligations of U.S. Government sponsored enterprises	Mar. 31, 2013 Recurring basis Significant Other Observable Inputs (Level 2) Obligations of states and political subdivisions	Mar. 31, 2013 Recurring basis Significant Other Observable Inputs (Level 2) Residential mortgage-backed securities	Mar. 31, 2013 Recurring basis Significant Unobservable Inputs (Level 3)	Mar. 31, 2013 Recurring basis Significant Unobservable Inputs (Level 3) Obligations of U.S. Government sponsored enterprises	Mar. 31, 2013 Recurring basis Significant Unobservable Inputs (Level 3) Obligations of states and political subdivisions	Mar. 31, 2013 Recurring basis Significant Unobservable Inputs (Level 3) Residential mortgage-backed securities	Mar. 31, 2013 Recurring basis Total Fair Value	Mar. 31, 2013 Recurring basis Total Fair Value Obligations of U.S. Government sponsored enterprises	Mar. 31, 2013 Recurring basis Total Fair Value Obligations of states and political subdivisions	Mar. 31, 2013 Recurring basis Total Fair Value Residential mortgage-backed securities	Mar. 31, 2013 Portion at Fair Value, Fair Value Disclosure Recurring basis Total Fair Value	Mar. 31, 2013 Portion at Other than Fair Value, Fair Value Disclosure	Mar. 31, 2013 LIBOR Swap Curve
Assets
Securities available for sale	$ 483,007	$ 640,212	$ 133,547	$ 152,368	$ 51,907	$ 53,003	$ 297,553	$ 434,841										$ 0	$ 0	$ 0	$ 0	$ 479,956	$ 133,547	$ 48,856	$ 297,553	$ 3,051	$ 0	$ 3,051	$ 0	$ 483,007	$ 133,547	$ 51,907	$ 297,553
Portfolio loans																		0				9,794				0				9,794
State tax credits held for sale	20,053	23,020							0	0	0	0	40,850	43,802		40,850	43,802	0				0				20,053				20,053				20,000	35,900
Derivative financial instruments																		0				1,622				0				1,622
Total assets																		0				491,372				23,104				514,476
Liabilities
Derivative financial instruments																		0				1,721				0				1,721
Total liabilities																		0				1,721				0				1,721
Number of securities															3
State tax credits, held for sale	$ 55,923	$ 61,284
Tax credit stream, term	10 years
Years of tax credits generated	10 years
Discount rate, remaining life in years of credits plus																																				20500.00%