Shares Underlying Stock Options, Excluded from Calculation of Weighted Average Number of Shares Outstanding used for Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of anti-dilutive potential shares	16,168	13,681	11,722
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of anti-dilutive potential shares	15,592	13,681	11,722
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of anti-dilutive potential shares	576