Other Comprehensive Income (Loss) - Summary of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized gains (losses) arising during the period, before U.S. income taxes	$ 10,531	$ (5,009)	$ 54,937	$ (30,934)
U.S. income taxes	(690)	425	(4,045)	1,124
Unrealized gains (losses) arising during the period, net of U.S. income taxes	9,841	(4,584)	50,892	(29,810)
Less reclassification adjustment:
Net realized investment gains (losses)	436	(213)	539	(306)
U.S. income taxes	(52)	18	(96)	(10)
Reclassification adjustment for investment gains (losses) realized in net income	384	(195)	443	(316)
Other comprehensive income (loss)	$ 9,457	$ (4,389)	$ 50,449	$ (29,494)