Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets:
Arbitrage trading account	$ 488,238	$ 299,999
Loans receivable	76,615	108,299
Carrying Value
Assets:
Fixed maturity securities	13,873,690	13,190,668
Equity securities available for sale	614,025	669,200
Arbitrage trading account	488,238	299,999
Loans receivable	74,229	106,798
Cash and cash equivalents	773,997	795,285
Trading account receivables from brokers and clearing organizations	297,208	484,593
Liabilities:
Due to broker	58,973	19,416
Trading account securities sold but not yet purchased	44,937	51,179
Subordinated debentures	728,071	727,630
Senior notes and other debt	1,759,929	1,760,595
Fair Value
Assets:
Fixed maturity securities	13,890,354	13,204,814
Equity securities available for sale	614,025	669,200
Arbitrage trading account	488,238	299,999
Loans receivable	76,615	108,299
Cash and cash equivalents	773,997	795,285
Trading account receivables from brokers and clearing organizations	297,208	484,593
Liabilities:
Due to broker	58,973	19,416
Trading account securities sold but not yet purchased	44,937	51,179
Subordinated debentures	728,291	687,504
Senior notes and other debt	$ 1,946,700	$ 1,914,727

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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 Fair Value

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