Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets:
Arbitrage trading account	$ 299,999	$ 376,697
Loans receivable	108,299	275,747
Due To Broker	19,416	0
Due To Broker Fair Value	19,416	0
Carrying Value
Assets:
Fixed maturity securities	13,190,668	12,444,394
Equity securities available for sale	669,200	150,866
Arbitrage trading account	299,999	376,697
Loans receivable	106,798	273,103
Cash and cash equivalents	795,285	763,631
Trading accounts receivable from brokers and clearing organizations	484,593	383,115
Due from broker	0	1,713
Liabilities:
Trading account securities sold but not yet purchased	51,179	37,035
Subordinated debentures	727,630	340,320
Senior notes and other debt	1,760,595	1,844,621
Fair Value
Assets:
Fixed maturity securities	13,204,814	12,462,847
Equity securities available for sale	669,200	150,866
Arbitrage trading account	299,999	376,697
Loans receivable	108,299	275,747
Cash and cash equivalents	795,285	763,631
Trading accounts receivable from brokers and clearing organizations	484,593	383,115
Due from broker	0	1,713
Liabilities:
Trading account securities sold but not yet purchased	51,179	37,035
Subordinated debentures	687,504	355,880
Senior notes and other debt	$ 1,914,727	$ 2,029,572

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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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