Other Comprehensive Income (Loss) - Summary of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized gains (losses) arising during the period, before U.S. income taxes	$ 22,928	$ (6,633)	$ 44,406	$ (25,925)
U.S. income taxes	(1,908)	155	(3,355)	699
Unrealized gains (losses) arising during the period, net of U.S. income taxes	21,020	(6,478)	41,051	(25,226)
Less reclassification adjustment:
Net realized investment gains (losses)	331	108	103	(93)
U.S. income taxes	(43)	(28)	(44)	(28)
Reclassification adjustment for investment gains (losses) realized in net income	288	80	59	(121)
Other comprehensive income (loss)	$ 20,732	$ (6,558)	$ 40,992	$ (25,105)