Reconciliation of Numerator and Denominator Used in Computation of Basic and Diluted Net Income Loss per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator for Basic and Diluted:
Net loss used for basic calculation	$ (59,857)	$ (71,244)	$ (57,564)
Denominator:
Basic weighted average number of shares outstanding	163,949	139,831	131,663
Diluted weighted average number of shares outstanding	163,949	139,831	131,663
Net loss per share:
Basic and diluted	$ (0.37)	$ (0.51)	$ (0.44)