Fair Value Measurements - Financial Instruments Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Assets
Securities available for sale	$ 471,017	$ 640,212
State tax credits held for sale	19,822	23,020
Liabilities
State tax credits, held for sale	55,493	61,284
Tax credit stream, term	10 years
Years of tax credits generated	10 years
Obligations of U.S. Government sponsored enterprises
Assets
Securities available for sale	130,720	152,368
Obligations of states and political subdivisions
Assets
Securities available for sale	50,984	53,003
Residential mortgage-backed securities
Assets
Securities available for sale	289,313	434,841
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
State tax credits held for sale	0	0
Significant Other Observable Inputs (Level 2)
Assets
State tax credits held for sale	0	0
Significant Unobservable Inputs (Level 3)
Assets
State tax credits held for sale	40,002	43,802
Significant Unobservable Inputs (Level 3) \| Auction Rate Securities
Liabilities
Number of securities	3
Total Fair Value
Assets
State tax credits held for sale	40,002	43,802
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Securities available for sale	0
Portfolio loans	0
State tax credits held for sale	0
Derivative financial instruments	0
Total assets	0
Liabilities
Derivative financial instruments	0
Total liabilities	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Obligations of U.S. Government sponsored enterprises
Assets
Securities available for sale	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Obligations of states and political subdivisions
Assets
Securities available for sale	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Residential mortgage-backed securities
Assets
Securities available for sale	0
Recurring basis \| Significant Other Observable Inputs (Level 2)
Assets
Securities available for sale	467,978
Portfolio loans	4,429
State tax credits held for sale	0
Derivative financial instruments	820
Total assets	473,227
Liabilities
Derivative financial instruments	836
Total liabilities	836
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Obligations of U.S. Government sponsored enterprises
Assets
Securities available for sale	130,720
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Obligations of states and political subdivisions
Assets
Securities available for sale	47,945
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Residential mortgage-backed securities
Assets
Securities available for sale	289,313
Recurring basis \| Significant Unobservable Inputs (Level 3)
Assets
Securities available for sale	3,039
Portfolio loans	0
State tax credits held for sale	19,822
Derivative financial instruments	0
Total assets	22,861
Liabilities
Derivative financial instruments	0
Total liabilities	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Obligations of U.S. Government sponsored enterprises
Assets
Securities available for sale	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Obligations of states and political subdivisions
Assets
Securities available for sale	3,039
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Residential mortgage-backed securities
Assets
Securities available for sale	0
Recurring basis \| Total Fair Value
Assets
Securities available for sale	471,017
Portfolio loans	4,429
State tax credits held for sale	19,822
Derivative financial instruments	820
Total assets	496,088
Liabilities
Derivative financial instruments	836
Total liabilities	836
Recurring basis \| Total Fair Value \| Obligations of U.S. Government sponsored enterprises
Assets
Securities available for sale	130,720
Recurring basis \| Total Fair Value \| Obligations of states and political subdivisions
Assets
Securities available for sale	50,984
Recurring basis \| Total Fair Value \| Residential mortgage-backed securities
Assets
Securities available for sale	289,313
Portion at Fair Value, Fair Value Disclosure \| Recurring basis \| Total Fair Value
Assets
State tax credits held for sale	19,800
Portion at Other than Fair Value, Fair Value Disclosure
Assets
State tax credits held for sale	$ 35,700
LIBOR Swap Curve
Liabilities
Discount rate, remaining life in years of credits plus	20500.00%

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This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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