Fair Value Disclosures (Fair Value Assets And Liabilities Measured On Recurring Basis) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands	Sep. 30, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	$ 15,424
Obligations of U. S. government sponsored-enterprises and agencies	251,521
Obligations of states and political subdivisions	632,789
Corporate bonds	116,098
Mortgage-backed securities	708,933
Other securities	3,792
Total	1,728,557
Level 1 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	15,424
Obligations of U. S. government sponsored-enterprises and agencies	5,393
Obligations of states and political subdivisions	29,904
Corporate bonds	34,839
Mortgage-backed securities	6,421
Other securities	3,792
Total	95,773
Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations of U. S. government sponsored-enterprises and agencies	246,128
Obligations of states and political subdivisions	602,885
Corporate bonds	81,259
Mortgage-backed securities	702,512
Total	1,632,784
Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities
Obligations of U. S. government sponsored-enterprises and agencies
Obligations of states and political subdivisions
Corporate bonds
Mortgage-backed securities
Other securities
Total

- 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 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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