Other Comprehensive Income - Summary of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized gains (losses) arising during the period, before U.S. income taxes	$ 909	$ (802)	$ 14,760	$ 31,662
U.S. income taxes	21	(38)	(2,771)	(3,115)
Unrealized gains (losses) arising during the period, net of U.S. income taxes	930	(840)	11,989	28,547
Less reclassification adjustment:
Net realized investment gains	329	1,243	767	2,651
U.S. income tax expenses	(115)	(411)	(236)	(844)
Reclassification adjustment for investment gains realized in net income	214	832	531	1,807
Other comprehensive income (loss)	$ 716	$ (1,672)	$ 11,458	$ 26,740