Fair Value Measurement (Level 3 Assets and Liability) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 27,996	$ 10,663	$ 11,958	$ 11,157
Gains Losses By Earnings Category Assets [Abstract]
Included in other comprehensive income	(7)	(64)	(73)	61
Purchases	26,047	9,413	62,285	14,241
Sales	(301)	(115)	(6,697)	(3,061)
Transfers in	69		3,079	1,550
Transfers out	(15,640)	(3,089)	(32,242)	(7,138)
Ending balance	37,523	16,949	37,523	16,949
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	(640)	143	(775)	151
Net investment income
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings			(1)	(10)
Net realized investment gains (losses)
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings	(641)	141	(786)	149
Corporate Debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	15,065	3,117	3,265	5,079
Gains Losses By Earnings Category Assets [Abstract]
Included in other comprehensive income	49	(6)	82	38
Purchases	10,881	900	24,971	900
Sales	(284)	(16)	(461)	(2,173)
Transfers in	0		858	945
Transfers out	(5,999)	0	(9,004)	(794)
Ending balance	19,712	3,995	19,712	3,995
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Corporate Debt \| Net investment income
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings			1	0
Corporate Debt \| Net realized investment gains (losses)
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings	0	0	0	0
Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	9,857	5,978	8,693	2,992
Gains Losses By Earnings Category Assets [Abstract]
Included in other comprehensive income	(74)	(58)	(171)	23
Purchases	12,666	8,513	28,026	13,341
Sales	(17)	(99)	(506)	(888)
Transfers in	0		0	605
Transfers out	(7,190)	(1,378)	(20,787)	(3,107)
Ending balance	15,242	12,954	15,242	12,954
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Asset-backed Securities \| Net investment income
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings			(2)	(10)
Asset-backed Securities \| Net realized investment gains (losses)
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings	0	(2)	(11)	(2)
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	852		0
Gains Losses By Earnings Category Assets [Abstract]
Included in other comprehensive income	18		16
Purchases	2,500		9,083
Sales	0		(5,730)
Transfers in	69		69
Transfers out	(868)		(868)
Ending balance	2,569		2,569
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	(1)		(1)
Equity securities \| Net investment income
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings			0
Equity securities \| Net realized investment gains (losses)
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings	(2)		(1)
Other Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	2,222	1,568	0	3,086
Gains Losses By Earnings Category Assets [Abstract]
Included in other comprehensive income	0	0	0	0
Purchases	0	0	205	0
Sales	0	0	0	0
Transfers in	0		2,152	0
Transfers out	(1,583)	(1,711)	(1,583)	(3,237)
Ending balance	0	0	0	0
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	(639)	143	(774)	151
Other Investments \| Net investment income
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings			0	0
Other Investments \| Net realized investment gains (losses)
Gains Losses By Earnings Category Assets [Abstract]
Total gains (losses) realized and unrealized, included in earnings	$ (639)	$ 143	$ (774)	$ 151

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Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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