Investments - Summary of Realized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investments [Abstract]
Fixed maturity securities, gross realized gains	$ 215	$ 177
Fixed maturity securities, gross realized losses	(1)	(405)
Fixed maturity securities	214	(228)
Bank loan participations, gross realized gains	103	13
Bank loan participations, gross realized losses	(1,309)	(1,692)
Changes in fair values of bank loan participations	(43,947)	0
Bank loan participations	(45,153)	(1,679)
Equity securities, gross realized gain	0	0
Equity securities, gross realized losses	(170)	(18)
Equity securities, changes in fair values of equity securities	(13,315)	3,549
Equity securities	(13,485)	3,531
Short-term investments and other, gross realized gains	18	1
Short-term investments and other, gross realized losses	(1)	0
Short-term investments and other	17	1
Total	$ (58,407)	$ 1,625