Basic and Diluted Net Loss Per Share of Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (1,534)	$ (4,618)	$ (9,179)	$ (16,976)
Denominator:
Weighted average shares outstanding, basic and diluted	44,718,597	43,202,751	44,559,368	43,153,598
Net loss per share, basic and diluted:	$ (0.03)	$ (0.11)	$ (0.21)	$ (0.39)
Antidilutive securities excluded from calculations of diluted net loss per share	3,409,711	5,804,031	3,285,106	6,024,656