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Goodwill and Other Intangibles - Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Millions | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Finite-Lived Intangible Assets [Line Items] |  |
Gross Amount | $ 880.4 | $ 585.4
Accumulated Amortization | (129.2) | (113.4)
Net Balance | 751.2 | 472.0
Noncompetition agreements |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Amount | 4.2 | 4.2
Accumulated Amortization | (4.1) | (4.1)
Net Balance | 0.1 | 0.1
Customer Relationships |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Amount | 312.7 | 91.3
Accumulated Amortization | (44.3) | (35.6)
Net Balance | 268.4 | 55.7
Operating Permits |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Amount | 523.8 | 460.8
Accumulated Amortization | (53.7) | (48.4)
Net Balance | 470.1 | 412.4
Use Rights And Other |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Amount | 16.4 | 16.3
Accumulated Amortization | (13.8) | (13.0)
Net Balance | 2.6 | 3.3
Trade names |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Amount | 23.3 | 12.8
Accumulated Amortization | (13.3) | (12.3)
Net Balance | $ 10.0 | $ 0.5

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