Net Income (Loss) Per Share - Summary of Potentially Dilutive Securities (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	31,727,069	42,314,596	33,973,292
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	1,810,580	3,369,732	5,818,435
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	10,201,660	11,403,341	12,222,282
ESPP obligations
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	317,940	361,688	366,529
2018 Notes | Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	0	7,782,946	7,783,023
2022 Notes | Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	5,806,933	5,806,933	0
2018 Warrants | Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	7,783,023	7,783,023	7,783,023
2022 Warrants | Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	5,806,933	5,806,933	0