Investments - Schedule of Available-for-sale Securities Reconciliation (Details) (USD $)	9 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Available for sale securities:
Amortized Cost	$ 595,433,000	$ 587,555,000
Gross Unrealized Gains	15,486,000	7,676,000
Gross Unrealized Losses	(562,000)	(2,049,000)
Fair Value	610,357,000	593,182,000
Percentage of shareholders' equity held by one issuer, maximum		10.00%
Available-for-sale securities pledged as collateral, fair value	271,800,000	287,800,000
Mortgage-backed securities, weighted average life	3 years
Obligations of U.S. Government sponsored enterprises
Available for sale securities:
Amortized Cost	124,721,000	126,305,000
Gross Unrealized Gains	3,284,000	678,000
Gross Unrealized Losses	0	(66,000)
Fair Value	128,005,000	126,917,000
Obligations of states and political subdivisions
Available for sale securities:
Amortized Cost	43,720,000	38,489,000
Gross Unrealized Gains	2,429,000	1,729,000
Gross Unrealized Losses	(360,000)	(381,000)
Fair Value	45,789,000	39,837,000
Residential mortgage-backed securities
Available for sale securities:
Amortized Cost	426,992,000	422,761,000
Gross Unrealized Gains	9,773,000	5,269,000
Gross Unrealized Losses	(202,000)	(1,602,000)
Fair Value	$ 436,563,000	$ 426,428,000

Amount of available-for-sale debt securities at cost, net of adjustments, which include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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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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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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