Net Loss Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss attributable to common stockholders	$ (21.0)	$ (23.1)	$ (57.5)	$ (44.7)
Denominator:
Weighted average common shares outstanding—basic and diluted (shares)	11,891,979	11,072,985	11,750,198	11,028,667
Net loss per share attributable to common stockholders—basic and diluted (usd per share)	$ (1.77)	$ (2.09)	$ (4.89)	$ (4.05)