Fair Value Of Financial Instruments (Quantitative Information related To The Significant Unobservable Inputs Utilized In Company's Level 3 Recurring Fair Value Measurements) (Details) (USD $)	3 Months Ended
Mar. 31, 2012	Dec. 31, 2011
Available-for-sale securities, Estimated fair value	$ 1,347,535,000	$ 1,214,141,000
Investments, Fair Value Disclosure	216,106,000	211,208,000
State And Municipal Securities [Member]
Available-for-sale securities, Estimated fair value	83,486,000	86,932,000
Discount rate, weighted average	5.00%
Auction Rate Equity Securities [Member]
Investments, Fair Value Disclosure	4.7	103,176,000
Auction Rate Municipal Securities [Member]
Investments, Fair Value Disclosure	4.2	11,729,000
Level 3 [Member]
Available-for-sale securities, Estimated fair value	76,859,000	78,896,000
Investments, Fair Value Disclosure	143,463,000	151,938,000
Level 3 [Member] \| State And Municipal Securities [Member]
Available-for-sale securities, Estimated fair value	64,859,000	66,896,000
Workout period range, low end	3
Workout period range, high end	4
Discount rate range, low end	2.40%
Discount rate range, high end	9.20%
Level 3 [Member] \| Auction Rate Equity Securities [Member]
Investments, Fair Value Disclosure		103,176,000
Workout period range, low end	1
Workout period range, high end	4
Discount rate range, low end	0.00%
Discount rate range, high end	7.50%
Level 3 [Member] \| Auction Rate Municipal Securities [Member]
Investments, Fair Value Disclosure		11,729,000
Workout period range, low end	1
Workout period range, high end	3
Discount rate range, low end	1.50%
Discount rate range, high end	8.70%
Estimated Fair Value [Member] \| State And Municipal Securities [Member]
Available-for-sale securities, Estimated fair value	64,859,000
Estimated Fair Value [Member] \| Auction Rate Equity Securities [Member]
Investments, Fair Value Disclosure	92,077,000
Estimated Fair Value [Member] \| Auction Rate Municipal Securities [Member]
Investments, Fair Value Disclosure	$ 13,404,000

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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