Investments - Summary of Realized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Net realized investment gains	$ (171)	$ 210	$ 1,183	$ 2,376
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	378	70	734	1,479
Gross realized losses	(4)	0	(331)	(2)
Net realized investment gains	374	70	403	1,477
Bank loan participations
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	341	273	1,948	1,466
Gross realized losses	(839)	(1,308)	(1,528)	(1,741)
Net realized investment gains	(498)	(1,035)	420	(275)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	0	1,174	409	1,174
Gross realized losses	(45)	0	(45)	0
Net realized investment gains	(45)	1,174	364	1,174
Short-term investments and other
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	1	2	1	3
Gross realized losses	(3)	(1)	(5)	(3)
Net realized investment gains	$ (2)	$ 1	$ (4)	$ 0