Other income, net - Schedule of Other Income Net (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Interest income	$ 469	$ 236	$ 1,093	$ 720
Foreign exchange (losses) gains	(3)	8	(34)	(12)
Miscellaneous expenses (Note 10)	(262)	(7)	(433)	(36)
Other income, net	$ 204	$ 237	$ 626	$ 672

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

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