Debt And Equity Securities (Available-For-Sale Investments Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	$ 2,403,951	$ 2,385,911
Level 1 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	217,828	184,000
Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	2,155,186	2,171,277
Level 3 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	30,937	30,634
Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	2,186,123	2,201,911
Debt Securities [Member] \| Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	2,155,186	2,171,277
Debt Securities [Member] \| Level 3 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	30,937	30,634
Debt Securities [Member] \| U.S. Treasury Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	110,062	74,231
Debt Securities [Member] \| U.S. Treasury Bonds [Member] \| Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	110,062	74,231
Debt Securities [Member] \| Municipal Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	374,711	349,123
Debt Securities [Member] \| Municipal Bonds [Member] \| Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	374,711	349,123
Debt Securities [Member] \| Foreign Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	226,415	215,020
Debt Securities [Member] \| Foreign Bonds [Member] \| Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	226,415	215,020
Debt Securities [Member] \| Governmental Agency Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	173,786	197,753
Debt Securities [Member] \| Governmental Agency Bonds [Member] \| Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	173,786	197,753
Debt Securities [Member] \| Governmental Agency Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	997,354	1,076,547
Debt Securities [Member] \| Governmental Agency Mortgage-Backed Securities [Member] \| Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	997,354	1,076,547
Debt Securities [Member] \| Non-Agency Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	30,937	30,634
Debt Securities [Member] \| Non-Agency Mortgage-Backed Securities [Member] \| Level 3 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	30,937	30,634
Debt Securities [Member] \| Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	272,858	258,603
Debt Securities [Member] \| Corporate Debt Securities [Member] \| Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	272,858	258,603
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	217,828	184,000
Equity Securities [Member] \| Preferred Stocks [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	7,692	7,668
Equity Securities [Member] \| Common Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	210,136	176,332
Equity Securities [Member] \| Level 1 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	217,828	184,000
Equity Securities [Member] \| Level 1 [Member] \| Preferred Stocks [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	7,692	7,668
Equity Securities [Member] \| Level 1 [Member] \| Common Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated fair value	$ 210,136	$ 176,332

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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