Goodwill - Summary of Goodwill Activity (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill Beginning Balance, Gross	$ 21.3	$ 21.3
No activity in period		0.0
Impairment	(9.5)
Goodwill Ending Balance, Gross	21.3	21.3
Accumulated Impairments	(21.3)	(11.8)	$ (11.8)	$ (11.8)
Goodwill Beginning Balance, Net	9.5	9.5
Goodwill Ending Balance, Net	$ 0.0	$ 9.5