Net Loss Per Share - Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Denominator
Weighted-average common shares outstanding - basic and diluted (in shares)	48,840,131	46,731,663	48,188,183	46,048,037
Basic and diluted net loss per share (in dollars per share)	$ (0.22)	$ (0.34)	$ (0.85)	$ (0.69)
Class A Common Stock
Numerator
Net loss	$ (8,691)	$ (12,978)	$ (33,617)	$ (25,422)
Denominator
Weighted-average common shares outstanding - basic and diluted (in shares)	40,400,270	37,785,850	39,661,228	36,771,232
Basic and diluted net loss per share (in dollars per share)	$ (0.22)	$ (0.34)	$ (0.85)	$ (0.69)
Class B Common Stock
Numerator
Net loss	$ (1,816)	$ (3,073)	$ (7,228)	$ (6,414)
Denominator
Weighted-average common shares outstanding - basic and diluted (in shares)	8,439,861	8,945,813	8,526,955	9,276,805
Basic and diluted net loss per share (in dollars per share)	$ (0.22)	$ (0.34)	$ (0.85)	$ (0.69)