Condensed summary of significant accounting policies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) Segment	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Foreign exchange loss and others	$ (31)	$ (468)
Effect of exchange rate changes on cash and cash equivalents	$ 41	(455)
Operating segment | Segment	1
Total Assets	$ 108,214		$ 113,343
Accumulated deficit	(117,987)		(111,276)
Reclassifications [Member]
Significant Accounting Policies [Line Items]
Foreign exchange loss and others		$ 455
United States [Member]
Significant Accounting Policies [Line Items]
Total Assets	$ 103,927		$ 111,366