Net (loss) income per share - Basic and Diluted Net (Loss) Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Computation of basic and diluted net income (loss) per share:
Net (loss) income	$ (22,786)	$ (16,902)	$ (15,031)	$ 13,138	$ (23,010)	$ (37,990)	$ (54,719)	$ (47,862)
Weighted average shares outstanding - basic	179,861			169,510			174,524	147,766
Weighted average shares outstanding - diluted	179,861			169,760			174,524	147,766
Net (loss) income per share-basic	$ (0.13)			$ 0.08			$ (0.31)	$ (0.32)
Net (loss) income per share-diluted	$ (0.13)			$ 0.08			$ (0.31)	$ (0.32)
Restricted stock units
Computation of basic and diluted net income (loss) per share:
Effect of dilutive securities				137
Stock options
Computation of basic and diluted net income (loss) per share:
Effect of dilutive securities				86
Employee Stock Purchase Plan
Computation of basic and diluted net income (loss) per share:
Effect of dilutive securities				27