Net income (loss) per share - Computation of Basic and Diluted Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income (loss)	$ 2,272	$ (8,125)	$ (19,145)	$ (36,908)
Weighted average shares used to compute per share amount:
Basic (in shares)	47,666	45,476	46,949	44,804
Diluted (in shares)	48,615	45,476	46,949	44,804
Basic net income (loss) per share (in dollars per share)	$ 0.05	$ (0.18)	$ (0.41)	$ (0.82)
Diluted net income (loss) per share (in dollars per share)	$ 0.05	$ (0.18)	$ (0.41)	$ (0.82)