Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Arbitrage trading account	$ 614,721	$ 341,473
Loans receivable	78,504	86,596
Carrying Value
Assets:
Fixed maturity securities	15,400,118	14,159,369
Equity securities	621,629	625,667
Arbitrage trading account	614,721	341,473
Loans receivable	76,896	84,913
Cash and cash equivalents	2,014,911	2,372,366
Trading account receivables from brokers and clearing organizations	257,756	524,727
Due from broker	0	2,585
Liabilities:
Due to broker	149,295	0
Trading account securities sold but not yet purchased	218	10,048
Senior notes and other debt	2,021,142	1,623,025
Subordinated debentures	1,289,272	1,102,309
Fair Value
Assets:
Fixed maturity securities	15,412,192	14,173,629
Equity securities	621,629	625,667
Arbitrage trading account	614,721	341,473
Loans receivable	78,504	86,596
Cash and cash equivalents	2,014,911	2,372,366
Trading account receivables from brokers and clearing organizations	257,756	524,727
Due from broker	0	2,585
Liabilities:
Due to broker	149,295	0
Trading account securities sold but not yet purchased	218	10,048
Senior notes and other debt	2,191,022	1,892,444
Subordinated debentures	$ 1,364,002	$ 1,202,842

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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-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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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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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 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 From Brokers, Fair Value Disclosure

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Due To Broker Fair Value

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Marketable Securities, Fair Value Disclosure

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Trading Accounts Receivable From Brokers, Fair Value Disclosure

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