Net Income (Loss) per Share - Computation of Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator
Net income (loss)	$ (12,625)	$ 3,207	$ (79,804)	$ (33,232)
Weighted average shares:
Basic (in shares)	91,216,886	83,164,670	90,915,334	82,590,979
Dilutive shares from stock plans (in shares)	0	7,578,508	0	0
Dilutive (in shares)	91,216,886	90,743,178	90,915,334	82,590,979
Net income (loss) per share
Net income (loss) per share - basic (in dollars per share)	$ (0.14)	$ 0.04	$ (0.88)	$ (0.40)
Net income (loss) per share - diluted (in dollars per share)	$ (0.14)	$ 0.04	$ (0.88)	$ (0.40)