Fair Value of Financial Instruments (Estimated Fair Values Of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investments [Member]
Assets
Investments	$ 3,204,757	$ 3,180,095
Interest Rate Swap Agreements [Member]
Liabilities
Interest rate swap agreements	0	103
Equity Contract [Member]
Liabilities
Equity contracts	628	175
Secured Notes [Member]
Liabilities
Secured notes payable	$ 140,000	$ 140,000

Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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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 investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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