Investments (Rollforward of Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	$ 64,771
Additions for credit losses not previously recorded	816	$ 31,371
Change in allowance on securities with previous allowance	621
Reduction for securities sold during the period	(6,510)
Reduction for securities with credit losses due to intent to sell		(3,039)
Ending balance	59,698	28,332
United States Municipalities, States and Territories
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	2,844
Additions for credit losses not previously recorded	0	0
Change in allowance on securities with previous allowance	(53)
Reduction for securities sold during the period	0
Reduction for securities with credit losses due to intent to sell		0
Ending balance	2,791	0
Corporate Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	60,193
Additions for credit losses not previously recorded	705	28,332
Change in allowance on securities with previous allowance	1,327
Reduction for securities sold during the period	(6,510)
Reduction for securities with credit losses due to intent to sell		0
Ending balance	55,715	28,332
Commercial Mortgage Backed Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	0
Additions for credit losses not previously recorded	0	2,491
Change in allowance on securities with previous allowance	0
Reduction for securities sold during the period	0
Reduction for securities with credit losses due to intent to sell		(2,491)
Ending balance	0	0
Residential Mortgage Backed Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	1,734
Additions for credit losses not previously recorded	111	0
Change in allowance on securities with previous allowance	(653)
Reduction for securities sold during the period	0
Reduction for securities with credit losses due to intent to sell		0
Ending balance	1,192	0
Other Asset Backed Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning balance	0
Additions for credit losses not previously recorded	0	548
Change in allowance on securities with previous allowance	0
Reduction for securities sold during the period	0
Reduction for securities with credit losses due to intent to sell		(548)
Ending balance	$ 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=118955579&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=118955579&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=118939692&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=118942338&loc=SL82898722-210454

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