Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Arbitrage trading account	$ 617,649	$ 299,999
Loans receivable	82,047	108,299
Due To Broker	15,920	19,416
Due To Broker Fair Value	15,920	19,416
Carrying Value
Assets:
Fixed maturity securities	13,551,250	13,190,668
Equity securities available for sale	576,647	669,200
Arbitrage trading account	617,649	299,999
Loans receivable	79,684	106,798
Cash and cash equivalents	950,471	795,285
Trading accounts receivable from brokers and clearing organizations	189,280	484,593
Liabilities:
Trading account securities sold but not yet purchased	64,358	51,179
Subordinated debentures	728,218	727,630
Senior notes and other debt	1,769,052	1,760,595
Fair Value
Assets:
Fixed maturity securities	13,566,976	13,204,814
Equity securities available for sale	576,647	669,200
Arbitrage trading account	617,649	299,999
Loans receivable	82,047	108,299
Cash and cash equivalents	950,471	795,285
Trading accounts receivable from brokers and clearing organizations	189,280	484,593
Liabilities:
Trading account securities sold but not yet purchased	64,358	51,179
Subordinated debentures	769,060	687,504
Senior notes and other debt	$ 1,945,313	$ 1,914,727

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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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Due to broker.

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Due To Broker Fair Value

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