Goodwill - Summary of Goodwill Activity (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill Beginning Balance, Gross	$ 21.3	$ 21.3
Impairment		(9.5)
No activity in period	0.0
Goodwill Ending Balance, Gross	21.3	21.3
Accumulated Impairments	(21.3)	(21.3)	$ (21.3)	$ (11.8)
Goodwill Beginning Balance, Net	0.0	9.5
Goodwill Ending Balance, Net	$ 0.0	$ 0.0