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Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement [Line Items]
Net investment income earned	$ 68,511	$ 68,185	$ 34,444	$ 55,967	$ 57,594	$ 55,826	$ 58,505	$ 50,618	$ 227,107	$ 222,543	$ 195,336
Fixed Income Securities [Member]
Statement [Line Items]
Net investment income earned									203,926	203,255	178,104
Commercial Mortgage Loans [Member]
Statement [Line Items]
Net investment income earned									844	0	0
Equity Securities [Member]
Statement [Line Items]
Net investment income earned									9,286	6,996	7,764
Short-term Investments [Member]
Statement [Line Items]
Net investment income earned									1,821	6,653	3,472
Other Investment Portfolio [Member]
Statement [Line Items]
Net investment income earned									26,922	18,778	17,799
Investment Expenses [Member]
Statement [Line Items]
Net investment income earned									$ (15,692)	$ (13,139)	$ (11,803)

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 http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

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+ References

No definition available.

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