Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets:
Arbitrage trading account	$ 619,881	$ 329,077
Carrying Value
Assets:
Fixed maturity securities	11,612,047	11,943,956
Equity securities available for sale	338,907	376,022
Arbitrage trading account	619,881	329,077
Loans receivable	411,851	401,961
Cash and cash equivalents	966,326	905,670
Trading account receivables from brokers and clearing organizations	123,320	446,873
Due from broker	24,890	14,449
Liabilities:
Trading account securities sold but not yet purchased	88,489	121,487
Junior subordinated debentures	339,772	243,206
Senior notes and other debt	1,696,461	1,871,535
Fair Value
Assets:
Fixed maturity securities	11,628,850	11,968,376
Equity securities available for sale	338,907	376,022
Arbitrage trading account	619,881	329,077
Loans receivable	417,323	406,443
Cash and cash equivalents	966,326	905,670
Trading account receivables from brokers and clearing organizations	123,320	446,873
Due from broker	24,890	14,449
Liabilities:
Trading account securities sold but not yet purchased	88,489	121,487
Junior subordinated debentures	302,540	252,000
Senior notes and other debt	$ 1,887,751	$ 2,190,173

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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The fair value amount of long-term debt 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.

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Fair value portion of liabilities pertaining to principal and customer trading transactions, or which may be incurred with the objective of generating a profit from short-term fluctuations in price as part of an entity's market-making, hedging and proprietary trading. Examples include, but are not limited to, short positions in securities, derivatives and commodities.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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