Net Loss per Share - Calculation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Class of Stock [Line Items]
Net loss	$ (447)	$ (9,336)	$ (60,986)	$ (28,256)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	152,146	145,701	150,372	144,434
Basic and diluted net loss per share (in usd per share)	$ 0	$ (0.06)	$ (0.41)	$ (0.20)
Class A
Class of Stock [Line Items]
Net loss	$ (103)	$ (2,245)	$ (14,207)	$ (7,009)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	35,028	35,041	35,030	35,827
Basic and diluted net loss per share (in usd per share)	$ 0	$ (0.06)	$ (0.41)	$ (0.20)
Class B
Class of Stock [Line Items]
Net loss	$ (344)	$ (7,091)	$ (46,779)	$ (21,247)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	117,118	110,660	115,342	108,607
Basic and diluted net loss per share (in usd per share)	$ 0	$ (0.06)	$ (0.41)	$ (0.20)