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Investments (Pre-tax Net Investment Income Earned) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Statement [Line Items]
Net investment income earned	$ 288,155		$ 326,589		$ 227,107
Fixed Income Securities [Member]
Statement [Line Items]
Net investment income earned	259,918		209,709		203,926
Commercial Mortgage Loans [Member]
Statement [Line Items]
Net investment income earned	5,555		2,743		844
Equity Securities [Member]
Statement [Line Items]
Net investment income earned	13,554		15,920		9,286
Short-term Investments [Member]
Statement [Line Items]
Net investment income earned	3,997		260		1,821
Alternative Investments [Member]
Statement [Line Items]
Net investment income earned	23,003	$ 23,000	117,701	$ 117,700	26,504	$ 26,500
Other Investment [Member]
Statement [Line Items]
Net investment income earned	258		359		418
Investment Expenses [Member]
Statement [Line Items]
Net investment income earned	$ (18,130)		$ (20,103)		$ (15,692)

X

- Definition

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))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

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+ References

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