Investments - Summary of Realized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments [Abstract]
Fixed maturity securities, gross realized gains	$ 305	$ 411	$ 521	$ 588
Fixed maturity securities, gross realized losses	0	(80)	(1)	(485)
Fixed maturity securities	305	331	520	103
Bank loan participations, gross realized gains	230	137	332	150
Bank loan participations, gross realized losses	(9,669)	(1,308)	(10,978)	(3,000)
Changes in fair values of bank loan participations	26,570	0	(17,377)	0
Bank loan participations	17,131	(1,171)	(28,023)	(2,850)
Equity securities, gross realized gain	0	0	0	0
Equity securities, gross realized losses	0	0	(170)	(18)
Changes in fair values of equity securities	4,046	1,900	(9,269)	5,449
Equity securities	4,046	1,900	(9,439)	5,431
Short-term investments and other, gross realized gains	31	3	50	4
Short-term investments and other, gross realized losses	0	0	(2)	0
Changes in fair values of short-term investments and other	80	0	80	0
Short-term investments and other	111	3	128	4
Total	$ 21,593	$ 1,063	$ (36,814)	$ 2,688