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Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net Investment Income [Line Items]
Net investment income earned	$ 83,731	$ 34,444	$ 153,447	$ 90,411
Investment Expense	(5,469)	(3,388)	(9,096)	(6,796)
Fixed Income Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	52,608	51,079	105,431	101,332
Commercial Mortgage Loans [Member]
Net Investment Income [Line Items]
Net investment income earned	695	156	1,209	218
Equity Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	2,982	2,023	5,470	3,575
Short-Term Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	55	420	140	1,586
Other Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	32,860	(15,846)	50,293	(9,504)
Alternative Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	$ 29,900	$ (16,000)	$ 50,100	$ (9,700)

X

- Definition

Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
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-Section S99
-Paragraph 1
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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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