Investments - Summary of Realized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Net realized investment gains	$ 307	$ 1,619	$ 1,354	$ 2,166
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	18	568	356	1,410
Gross realized losses	(31)	(1)	(327)	(2)
Net realized investment gains	(13)	567	29	1,408
Bank loan participations
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	471	1,133	1,607	1,193
Gross realized losses	(150)	(81)	(689)	(433)
Net realized investment gains	321	1,052	918	760
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	0	0	409	0
Gross realized losses	0	0	0	0
Net realized investment gains	0	0	409	0
Short-term investments and other
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	0	1	0	1
Gross realized losses	(1)	(1)	(2)	(3)
Net realized investment gains	$ (1)	$ 0	$ (2)	$ (2)