Other Comprehensive Income - Summary of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized (losses) gains arising during the period, before U.S. income taxes	$ (19,292)	$ 5,998
U.S. income taxes	544	(1,636)
Unrealized (losses) gains arising during the period, net of U.S. income taxes	(18,748)	4,362
Less reclassification adjustment:
Net realized investment (losses) gains	(201)	450
U.S. income tax expenses	0	(122)
Reclassification adjustment for investment (losses) gains realized in net income	(201)	328
Other comprehensive (loss) income	$ (18,547)	$ 4,034

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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