Intangible Assets - Summary of Changes in Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets Net Excluding Goodwill [Abstract]
Balance at the beginning of the year	$ 11,601	$ 1,193
Changes in intangible assets	0	11,784
Amortization of intangible assets	(1,219)	(1,106)
Other, primarily impact from changes in foreign currency exchange rates	639	(270)
Balance at the end of the year	$ 11,021	$ 11,601