Net Loss Per Share - Summary of Potentially Dilutive Securities (Detail) - shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	45,728,575	36,031,853
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	4,992,394	6,902,902
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	13,270,087	13,274,438
ESPP obligations
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	286,176	288,467
2018 convertible senior notes | Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	7,783,023	7,783,023
2022 convertible senior notes | Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	5,806,936	0
Warrants related to the issuance of 2018 convertible senior notes | Warrants related to the issuance of convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	7,783,023	7,783,023
Warrants related to the issuance of 2022 convertible senior notes | Warrants related to the issuance of convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities	5,806,936	0