Investments - Summary of Realized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Fixed maturity securities, gross realized gains	$ 1,575	$ 422	$ 840
Fixed maturity securities, gross realized losses	(494)	(976)	(512)
Fixed maturity securities	1,081	(554)	328
Equity securities, gross realized gains	11	0	429
Equity securities, gross realized losses	(232)	(62)	(1,591)
Changes in fair values of equity securities	6,257	(5,970)	0
Equity securities	6,036	(6,032)	(1,162)
Bank loan participations, gross realized gain	846	2,279	2,407
Bank loan participations, gross realized losses	(10,902)	(1,166)	(3,557)
Bank loan participations	(10,056)	1,113	(1,150)
Short-term investments and other, gross realized gains	21	0	1
Short-term investments and other, gross realized losses	(1)	(6)	(6)
Short-term investments and other	20	(6)	(5)
Total	$ (2,919)	$ (5,479)	$ (1,989)