Other income, net - Schedule of Other Income Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Interest income	$ 1,563	$ 998	$ 619
Foreign exchange losses	(75)	(19)	(13)
Change in fair value of derivative liability			81
Miscellaneous expenses (Note 10)	(445)	(39)	(43)
Total Other income (expenses)	$ 1,043	$ 940	$ 644