Net Income (Loss) Per Share - Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net income (loss)	$ (1,545)	$ 10,622
Denominator:
Weighted-average shares outstanding - basic (in shares)	182,061,579	175,482,833
Weighted-average shares outstanding - diluted (in shares)	182,061,579	190,249,786
Net income (loss) per share - basic (in dollars per share)	$ (0.01)	$ 0.06
Net income (loss) per share - diluted (in dollars per share)	$ (0.01)	$ 0.06
Common stock options
Denominator:
Weighted-average effect of potentially dilutive securities (in shares)	0	1,995,185
RSUs
Denominator:
Weighted-average effect of potentially dilutive securities (in shares)	0	5,869,792
ESPP obligations
Denominator:
Weighted-average effect of potentially dilutive securities (in shares)	0	7,510
In-the-money portion of Notes | 2018 Notes
Denominator:
Weighted-average effect of potentially dilutive securities (in shares)	0	3,794,221
In-the-money portion of Notes | 2022 Notes
Denominator:
Weighted-average effect of potentially dilutive securities (in shares)	0	736,587
2018 Warrants | Warrants
Denominator:
Weighted-average effect of potentially dilutive securities (in shares)	0	2,363,658