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Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net Investment Income [Line Items]
Net investment income earned	$ 69,716	$ 55,967
Investment Expense	(3,627)	(3,408)
Fixed Income Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	52,823	50,253
Commercial Mortgage Loans [Member]
Net Investment Income [Line Items]
Net investment income earned	514	62
Equity Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	2,488	1,552
Short-Term Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	85	1,166
Other Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	17,433	6,342
Alternative Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	$ 20,200	$ 6,300

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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