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Investments (Other Investment Portfolio by Strategy and the Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Net investment income earned		$ 93,032	$ 68,185	$ 246,479	$ 158,596
Carrying Value		392,788		392,788		$ 266,322
Alternative Investments [Member]
Net investment income earned		42,800	$ 18,700	92,900	$ 8,900
Other Securities [Member]
Carrying Value		50,296		50,296		35,370
Remaining Commitment		0		0		0
Maximum Exposure to Loss	[1]	50,296		50,296		35,370
Alternative Investments [Member]
Carrying Value		342,492		342,492		230,952
Remaining Commitment		219,249		219,249		215,728
Maximum Exposure to Loss	[1]	561,741		561,741		446,680
Alternative Investments [Member] | Private Equity Funds [Member]
Carrying Value		257,160		257,160		157,276
Remaining Commitment		103,792		103,792		100,905
Maximum Exposure to Loss	[1]	360,952		360,952		258,181
Alternative Investments [Member] | Private Credit Funds [Member]
Carrying Value		62,462		62,462		54,017
Remaining Commitment		91,991		91,991		98,330
Maximum Exposure to Loss	[1]	154,453		154,453		152,347
Alternative Investments [Member] | Real Assets [Member]
Carrying Value		22,870		22,870		19,659
Remaining Commitment		23,466		23,466		16,493
Maximum Exposure to Loss	[1]	46,336		46,336		36,152
Other Investments [Member]
Carrying Value		392,788		392,788		266,322
Remaining Commitment		219,249		219,249		215,728
Maximum Exposure to Loss	[1]	$ 612,037		$ 612,037		$ 482,050
[1] The maximum exposure to loss includes both the carry value of these investments and the related remaining commitments. In addition, tax credits that have been previously recognized in Other securities are subject to the risk of recapture, which we do not consider significant.

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This item represents contractual obligations to invest additional amounts on our other investment portfolio. These additional investments may or may not be required.

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No definition available.

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(2))
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Amount of investments classified as other.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
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