Net Loss per Share Attributable to Common Stockholders - Schedule of Computation of Basic and Diluted Earnings per Share Attributable to Common Stockholders (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
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss attributable to common stockholders	$ (40,853)	$ (37,989)	$ (77,673)	$ (70,477)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	118,056	81,579	96,393	79,755
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.35)	$ (0.47)	$ (0.81)	$ (0.88)
Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss attributable to common stockholders		$ (37,989)		$ (70,477)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)		81,579		79,755
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)		$ (0.47)		$ (0.88)
Class A common stock | Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss attributable to common stockholders	$ (4,573)		$ (3,588)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	13,215		4,453
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.35)		$ (0.81)
Class B common stock | Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss attributable to common stockholders	$ (36,280)		$ (74,085)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	104,841		91,940
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.35)		$ (0.81)