Other Comprehensive Income - Summary of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized gains arising during the period, before U.S. income taxes	$ 7,853	$ 15,346	$ 13,851	$ 32,464
U.S. income taxes	(1,156)	(2,147)	(2,792)	(3,077)
Unrealized gains arising during the period, net of U.S. income taxes	6,697	13,199	11,059	29,387
Less reclassification adjustment:
Net realized investment gains	(12)	567	438	1,408
U.S. income tax expenses	1	(160)	(121)	(433)
Reclassification adjustment for investment gains realized in net income	(11)	407	317	975
Other comprehensive income	$ 6,708	$ 12,792	$ 10,742	$ 28,412