Computation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net loss	$ (45,700)	$ (2,500)	$ (700)	$ (5,000)	$ 1,600	$ 1,600	$ (1,100)	$ (2,600)	$ (53,907)	$ (522)	$ (2,382)
Denominator:
Weighted-average common shares (in thousands) - diluted									20,847	19,034	14,930
Basic and Diluted net loss per share	$ (2.17)	$ (0.12)	$ (0.03)	$ (0.24)	$ 0.08	$ 0.08	$ (0.06)	$ (0.16)	$ (2.59)	$ (0.03)	$ (0.16)