Net Loss Per Share - Reconciliation of Numerator and Denominators in Computing Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ (53,324)	$ (25,800)	$ (37,763)	$ (35,202)	$ (79,124)	$ (72,965)
Denominator:
Shares used in per share calculation (in shares)	55,355		42,458		51,770	42,348
Net loss per share, basic and diluted (in dollars per share)	$ (0.96)		$ (0.89)		$ (1.53)	$ (1.72)