Condensed summary of significant accounting policies - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) Segment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Foreign exchange loss and others	$ 48	$ 425
Effect of exchange rate changes on cash and cash equivalents	$ 31	(399)
Operating segment | Segment	1
Total Assets	$ 100,700		$ 113,343
Accumulated deficit	128,888		111,276
Reclassifications [Member]
Significant Accounting Policies [Line Items]
Foreign exchange loss and others		$ 399
United States [Member]
Significant Accounting Policies [Line Items]
Total Assets	$ 92,370		$ 111,366