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Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net Investment Income [Line Items]
Net investment income earned	$ 93,032	$ 68,185	$ 246,479	$ 158,596
Investment Expense	(5,218)	(4,208)	(14,314)	(11,004)
Fixed Income Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	51,683	51,285	157,114	152,617
Commercial Mortgage Loans [Member]
Net Investment Income [Line Items]
Net investment income earned	683	245	1,892	463
Equity Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	2,955	1,948	8,425	5,523
Short-Term Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	64	244	204	1,830
Other Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	42,865	18,671	93,158	9,167
Alternative Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	$ 42,800	$ 18,700	$ 92,900	$ 8,900

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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-Section S99
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