Goodwill and Other Intangible Assets - Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 560.4	$ 560.4
Accumulated Amortization	(101.9)	(88.8)
Net Balance	458.5	471.6
Noncompetition agreements
Finite-Lived Intangible Assets [Line Items]
Gross Amount	6.3	6.3
Accumulated Amortization	(6.2)	(6.2)
Net Balance	0.1	0.1
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Amount	65.6	65.6
Accumulated Amortization	(30.4)	(25.6)
Net Balance	35.2	40.0
Operating Permits
Finite-Lived Intangible Assets [Line Items]
Gross Amount	459.0	459.0
Accumulated Amortization	(42.3)	(36.1)
Net Balance	416.7	422.9
Use Rights And Other
Finite-Lived Intangible Assets [Line Items]
Gross Amount	16.7	16.7
Accumulated Amortization	(12.1)	(11.2)
Net Balance	4.6	5.5
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Amount	12.8	12.8
Accumulated Amortization	(10.9)	(9.7)
Net Balance	$ 1.9	$ 3.1