Net Loss Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss attributable to common stockholders	$ (66.4)	$ (30.9)	$ (171.0)	$ (88.4)
Denominator:
Weighted average common shares outstanding—basic (shares)	61,580,145	53,997,315	61,086,238	25,935,362
Weighted average common shares outstanding—diluted (shares)	61,580,145	53,997,315	61,086,238	25,935,362
Net loss per share attributable to common stockholders—basic (usd per share)	$ (1.08)	$ (0.57)	$ (2.80)	$ (3.41)
Net loss per share attributable to common stockholders—diluted (usd per share)	$ (1.08)	$ (0.57)	$ (2.80)	$ (3.41)