Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	$ 1,001,497	$ 831,749
Impaired loans	55,593	76,283
U.S. Treasury securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	104,656	46,035
Obligations of U.S. government corporations and agencies
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	370,194	349,031
Obligations of states and political subdivisions
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	280,288	154,437
Residential mortgage-backed securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	217,715	278,115
Corporate debt securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	24,714	2,583
Mutual funds and other equity securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	3,930	1,548
Recurring basis \| Level 1 Inputs
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	28,644	4,131
Recurring basis \| Level 1 Inputs \| Corporate debt securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	24,714	2,583
Recurring basis \| Level 1 Inputs \| Mutual funds and other equity securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	3,930	1,548
Recurring basis \| Level 2 Inputs
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	972,853	827,618
Recurring basis \| Level 2 Inputs \| U.S. Treasury securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	104,656	46,035
Recurring basis \| Level 2 Inputs \| Obligations of U.S. government corporations and agencies
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	370,194	349,031
Recurring basis \| Level 2 Inputs \| Obligations of states and political subdivisions
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	280,288	154,437
Recurring basis \| Level 2 Inputs \| Residential mortgage-backed securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	217,715	278,115
Recurring basis \| Total Fair Value
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	1,001,497	831,749
Recurring basis \| Total Fair Value \| U.S. Treasury securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	104,656	46,035
Recurring basis \| Total Fair Value \| Obligations of U.S. government corporations and agencies
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	370,194	349,031
Recurring basis \| Total Fair Value \| Obligations of states and political subdivisions
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	280,288	154,437
Recurring basis \| Total Fair Value \| Residential mortgage-backed securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	217,715	278,115
Recurring basis \| Total Fair Value \| Corporate debt securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	24,714	2,583
Recurring basis \| Total Fair Value \| Mutual funds and other equity securities
Financial assets and financial liabilities measured at fair value
Securities available-for-sale:	3,930	1,548
Non-recurring basis \| Level 3 Inputs
Financial assets and financial liabilities measured at fair value
Impaired loans	2,284	4,905
Foreclosed assets	511	794
Non-recurring basis \| Total Fair Value
Financial assets and financial liabilities measured at fair value
Impaired loans	2,284	4,905
Foreclosed assets	$ 511	$ 794

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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Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

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