Investments (Rollforward of Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	$ 59,698	$ 28,332	$ 64,771	$ 0
Additions for credit losses not previously recorded	0	25,041	816	56,412
Change in allowance on securities with previous allowance	176		797
Reduction for securities sold during the period	(44,248)		(50,758)
Recoveries of amounts previously written off	(1,436)		(1,436)
Reduction for securities with credit losses due to intent to sell		(3,187)		(6,226)
Ending balance	14,190	50,186	14,190	50,186
United States Municipalities, States and Territories
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	2,791	0	2,844	0
Additions for credit losses not previously recorded	0	0	0	0
Change in allowance on securities with previous allowance	556		503
Reduction for securities sold during the period	0		0
Recoveries of amounts previously written off	0		0
Reduction for securities with credit losses due to intent to sell		0		0
Ending balance	3,347	0	3,347	0
Corporate Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	55,715	28,332	60,193	0
Additions for credit losses not previously recorded	0	18,417	705	46,749
Change in allowance on securities with previous allowance	(402)		925
Reduction for securities sold during the period	(44,248)		(50,758)
Recoveries of amounts previously written off	(342)		(342)
Reduction for securities with credit losses due to intent to sell		0		0
Ending balance	10,723	46,749	10,723	46,749
Commercial Mortgage Backed Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	0	0	0	0
Additions for credit losses not previously recorded	0	5,847	0	8,338
Change in allowance on securities with previous allowance	0		0
Reduction for securities sold during the period	0		0
Recoveries of amounts previously written off	0		0
Reduction for securities with credit losses due to intent to sell		(3,187)		(5,678)
Ending balance	0	2,660	0	2,660
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	1,192	0	1,734	0
Additions for credit losses not previously recorded	0	777	111	777
Change in allowance on securities with previous allowance	22		(631)
Reduction for securities sold during the period	0		0
Recoveries of amounts previously written off	(1,094)		(1,094)
Reduction for securities with credit losses due to intent to sell		0		0
Ending balance	120	777	120	777
Other Asset Backed Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	0	0	0	0
Additions for credit losses not previously recorded	0	0	0	548
Change in allowance on securities with previous allowance	0		0
Reduction for securities sold during the period	0		0
Recoveries of amounts previously written off	0		0
Reduction for securities with credit losses due to intent to sell		0		(548)
Ending balance	$ 0	$ 0	$ 0	$ 0

Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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