Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets:
Arbitrage trading account	$ 533,442	$ 452,548
Loans receivable	96,905	97,073
Carrying Value
Assets:
Fixed maturity securities	13,732,800	13,606,812
Equity securities	416,588	279,006
Arbitrage trading account	533,442	452,548
Loans receivable	94,697	94,813
Cash and cash equivalents	1,258,174	817,602
Trading account receivables from brokers and clearing organizations	402,361	347,228
Liabilities:
Due to broker	39,230	20,144
Trading account securities sold but not yet purchased	159,349	38,120
Subordinated debentures	907,866	907,491
Senior notes and other debt	1,873,799	1,882,028
Fair Value
Assets:
Fixed maturity securities	13,746,972	13,619,620
Equity securities	416,588	279,006
Arbitrage trading account	533,442	452,548
Loans receivable	96,905	97,073
Cash and cash equivalents	1,258,174	817,602
Trading account receivables from brokers and clearing organizations	402,361	347,228
Liabilities:
Due to broker	39,230	20,144
Trading account securities sold but not yet purchased	159,349	38,120
Subordinated debentures	969,172	840,002
Senior notes and other debt	$ 2,019,430	$ 1,968,996

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

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- Definition

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

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- References

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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- Definition

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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- Definition

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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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Due To Broker Fair Value

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- Definition

Marketable Securities, Fair Value Disclosure

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Trading Accounts Receivable From Brokers, Fair Value Disclosure

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