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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Net loss	$ (4,204)	$ (8,381)	$ (60,539)	$ (18,920)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	150,078	144,572	149,475	143,790
Basic and diluted net loss per share (in usd per share)	$ (0.03)	$ (0.06)	$ (0.41)	$ (0.13)
Class A
Class of Stock [Line Items]
Net loss	$ (981)	$ (2,026)	$ (14,188)	$ (4,767)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	35,030	35,276	35,031	36,227
Basic and diluted net loss per share (in usd per share)	$ (0.03)	$ (0.06)	$ (0.41)	$ (0.13)
Class B
Class of Stock [Line Items]
Net loss	$ (3,223)	$ (6,355)	$ (46,351)	$ (14,153)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	115,048	109,296	114,444	107,563
Basic and diluted net loss per share (in usd per share)	$ (0.03)	$ (0.06)	$ (0.41)	$ (0.13)