Income Taxes - (Loss) Income Before Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
United States	$ (123.6)	$ (109.5)	$ (53.0)
Foreign	2.8	1.6	0.4
Loss before income taxes	$ (120.8)	$ (107.9)	$ (52.6)