Fair Value Measurement (Level 3 Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning balance	$ 11,675	$ 8,431	$ 11,157	$ 8,175
Included in earnings, as a part of:
Included in other comprehensive income	330	61	125	221
Purchases	1,406	170	4,828	1,475
Sales	(1,239)	(2,000)	(2,946)	(2,142)
Transfers in	0	418	1,550	1,618
Transfers out	(1,729)	0	(4,049)	(2,151)
Ending balance	10,663	7,091	10,663	7,091
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	230	0	8	0
Net investment income
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(10)	(22)	(10)	(138)
Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	230	33	8	33
Corporate Debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning balance	3,440	4,296	5,079	4,322
Included in earnings, as a part of:
Included in other comprehensive income	127	8	44	11
Purchases	0	0	0	1,305
Sales	(450)	(2,000)	(2,157)	(2,136)
Transfers in	0	0	945	0
Transfers out	0	0	(794)	(1,200)
Ending balance	3,117	2,304	3,117	2,304
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
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0	0	2
Corporate Debt | Net realized investment gains (losses)
Included in earnings, as a part of:
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:
Beginning balance	6,897	4,132	2,992	3,850
Included in earnings, as a part of:
Included in other comprehensive income	203	53	81	210
Purchases	1,406	0	4,828	0
Sales	(789)	0	(789)	(6)
Transfers in	0	0	605	1,200
Transfers out	(1,729)	0	(1,729)	(951)
Ending balance	5,978	4,163	5,978	4,163
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
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(10)	(22)	(10)	(140)
Asset-backed Securities | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0	0	0
Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning balance	1,338	3	3,086	3
Included in earnings, as a part of:
Included in other comprehensive income	0	0	0	0
Purchases	0	170	0	170
Sales	0	0	0	0
Transfers in	0	418	0	418
Transfers out	0	0	(1,526)	0
Ending balance	1,568	624	1,568	624
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	230	0	8	0
Other investments | Net investment income
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0	0	0
Other investments | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	$ 230	$ 33	$ 8	$ 33