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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Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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- Definition

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 Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

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Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Assets:
Investment securities, available-for-sale	$ 860,137	$ 880,764
Trading account securities	162	146
Mortgages held for sale	10,634	10,879
U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	405,841	422,253
U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	105,523	105,437
Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	309,799	312,407
Corporate debt securities
Assets:
Investment securities, available-for-sale	29,895	31,248
Foreign government and other securities
Assets:
Investment securities, available-for-sale	2,718	3,726
Total debt securities
Assets:
Investment securities, available-for-sale	853,776	875,071
Marketable equity securities
Assets:
Investment securities, available-for-sale	6,361	5,693
Recurring basis \| Level 1
Assets:
Investment securities, available-for-sale	26,432	25,756
Trading account securities	162	146
Total	26,594	25,902
Recurring basis \| Level 1 \| U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	20,071	20,063
Recurring basis \| Level 1 \| Total debt securities
Assets:
Investment securities, available-for-sale	20,071	20,063
Recurring basis \| Level 1 \| Marketable equity securities
Assets:
Investment securities, available-for-sale	6,361	5,693
Recurring basis \| Level 2
Assets:
Investment securities, available-for-sale	826,635	847,307
Mortgages held for sale	10,634	10,879
Total	851,918	874,312
Liabilities:
Total	14,937	16,444
Recurring basis \| Level 2 \| Interest rate swap contracts
Assets:
Accrued income and other assets	14,649	16,126
Liabilities:
Accrued expenses and other liabilities	14,937	16,444
Recurring basis \| Level 2 \| U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	385,770	402,190
Recurring basis \| Level 2 \| U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	98,453	97,736
Recurring basis \| Level 2 \| Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	309,799	312,407
Recurring basis \| Level 2 \| Corporate debt securities
Assets:
Investment securities, available-for-sale	29,895	31,248
Recurring basis \| Level 2 \| Foreign government and other securities
Assets:
Investment securities, available-for-sale	2,718	3,726
Recurring basis \| Level 2 \| Total debt securities
Assets:
Investment securities, available-for-sale	826,635	847,307
Recurring basis \| Level 3
Assets:
Investment securities, available-for-sale	7,070	7,701	9,934
Total	7,070	7,701
Recurring basis \| Level 3 \| U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	7,070	7,701
Recurring basis \| Level 3 \| Total debt securities
Assets:
Investment securities, available-for-sale	7,070	7,701
Recurring basis \| Total
Assets:
Investment securities, available-for-sale	860,137	880,764
Trading account securities	162	146
Mortgages held for sale	10,634	10,879
Total	885,582	907,915
Liabilities:
Total	14,937	16,444
Recurring basis \| Total \| Interest rate swap contracts
Assets:
Accrued income and other assets	14,649	16,126
Liabilities:
Accrued expenses and other liabilities	14,937	16,444
Recurring basis \| Total \| U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	405,841	422,253
Recurring basis \| Total \| U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	105,523	105,437
Recurring basis \| Total \| Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	309,799	312,407
Recurring basis \| Total \| Corporate debt securities
Assets:
Investment securities, available-for-sale	29,895	31,248
Recurring basis \| Total \| Foreign government and other securities
Assets:
Investment securities, available-for-sale	2,718	3,726
Recurring basis \| Total \| Total debt securities
Assets:
Investment securities, available-for-sale	853,776	875,071
Recurring basis \| Total \| Marketable equity securities
Assets:
Investment securities, available-for-sale	$ 6,361	$ 5,693