Securities (Details Textual) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Dec. 31, 2012 Securities	Mar. 31, 2012
Securities (Textual) [Abstract]
Number of securities holdings	0
Shareholders' equity percentage	10.00%
Number of structured pooled trust preferred securities deemed to be other-than-temporarily impaired	4	4
Adjusted amortized cost of one structured pooled trust preferred security held by the corporation	$ 738,857	$ 712,637
Fair value of one structured pooled trust preferred security held by the corporation	760,945	737,311
Securities	263,391	264,813
Pooled trust preferred [Member]
Securities (Textual) [Abstract]
Adjusted amortized cost of one structured pooled trust preferred security held by the corporation	800	800
Fair value of one structured pooled trust preferred security held by the corporation	558	600
Four Structured Pool Trust Securities [Member]
Securities (Textual) [Abstract]
Adjusted amortized cost of one structured pooled trust preferred security held by the corporation	0	0
Number of Pooled Trust Securities		1
Other than temporary impairment recognized in earnings for available for sale securities	$ 0		$ 0

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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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

The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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