Goodwill and Other Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,785,718	$ 2,769,332
Accumulated Amortization	2,012,059	1,972,984
Goodwill gross carrying amount	1,990,937	1,993,990
Goodwill accumulated amortization	253,536	253,536
Customer Lists and Contracts [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	582,156	586,055
Accumulated Amortization	$ 510,291	505,778
Customer Lists and Contracts [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated Life (Years)	7 years
Customer Lists and Contracts [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated Life (Years)	10 years
Non-competition Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 65,752	65,477
Accumulated Amortization	$ 64,062	63,924
Non-competition Agreements [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated Life (Years)	3 years
Non-competition Agreements [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated Life (Years)	15 years
Site Locations [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,091,912	2,072,059
Accumulated Amortization	$ 1,404,915	1,372,954
Site Locations [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated Life (Years)	15 years
Other [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 45,898	45,741
Accumulated Amortization	$ 32,791	$ 30,328
Other [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated Life (Years)	2 years
Other [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated Life (Years)	15 years