Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets
Securities available for sale	$ 400,146us-gaap_AvailableForSaleSecurities	$ 434,587us-gaap_AvailableForSaleSecurities
State tax credits held for sale	11,689	16,491
Portion at Other than Fair Value, Fair Value Disclosure
Assets
State tax credits held for sale	26,600
Total Fair Value
Assets
Securities available for sale	400,146	434,587
State tax credits held for sale	42,970	52,159
Derivative financial instruments	909	1,000
Liabilities
Derivative financial instruments	907	990
Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	91,826	93,530
Obligations of states and political subdivisions
Assets
Securities available for sale	34,881	48,943
Residential mortgage-backed securities
Assets
Securities available for sale	273,439	292,114
Recurring basis \| Total Fair Value
Assets
Securities available for sale	400,146	434,587
State tax credits held for sale	11,689	16,491
Derivative financial instruments	909	1,000
Total assets	412,744	452,078
Liabilities
Derivative financial instruments	907	990
Total liabilities	907	990
Recurring basis \| Obligations of U.S. Government-sponsored enterprises \| Total Fair Value
Assets
Securities available for sale	91,826	93,530
Recurring basis \| Obligations of states and political subdivisions \| Total Fair Value
Assets
Securities available for sale	34,881	48,943
Recurring basis \| Residential mortgage-backed securities \| Total Fair Value
Assets
Securities available for sale	273,439	292,114
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Securities available for sale	0	0
State tax credits held for sale	0	0
Derivative financial instruments	0	0
Total assets	0	0
Liabilities
Derivative financial instruments	0	0
Total liabilities	0	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	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	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Residential mortgage-backed securities
Assets
Securities available for sale	0	0
Recurring basis \| Significant Other Observable Inputs (Level 2)
Assets
Securities available for sale	397,087	431,547
State tax credits held for sale	0	0
Derivative financial instruments	909	1,000
Total assets	397,996	432,547
Liabilities
Derivative financial instruments	907	990
Total liabilities	907	990
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	91,826	93,530
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Obligations of states and political subdivisions
Assets
Securities available for sale	31,822	45,903
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Residential mortgage-backed securities
Assets
Securities available for sale	273,439	292,114
Recurring basis \| Significant Unobservable Inputs (Level 3)
Assets
Securities available for sale	3,059	3,040
State tax credits held for sale	11,689	16,491
Derivative financial instruments	0	0
Total assets	14,748	19,531
Liabilities
Derivative financial instruments	0	0
Total liabilities	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Obligations of states and political subdivisions
Assets
Securities available for sale	3,059	3,040
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Residential mortgage-backed securities
Assets
Securities available for sale	$ 0	$ 0

State Tax Credits Held For Sale, Fair Value Disclosure

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value of financial and nonfinancial obligations.

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