Net Loss Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss attributable to common stockholders	$ (122.3)	$ (108.5)	$ (52.9)
Denominator:
Weighted average common shares outstanding — basic and diluted	33,654,828	11,124,397	10,931,776
Net loss per share attributable to common stockholders — basic and diluted	$ (3.63)	$ (9.75)	$ (4.84)