Goodwill and Other Intangible Assets - Summary of Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified					3 Months Ended				3 Months Ended				3 Months Ended			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Customer lists and contracts [Member]	Dec. 31, 2012 Customer lists and contracts [Member]	Mar. 31, 2013 Customer lists and contracts [Member] Minimum [Member]	Mar. 31, 2013 Customer lists and contracts [Member] Maximum [Member]	Mar. 31, 2013 Non-competition agreements [Member]	Dec. 31, 2012 Non-competition agreements [Member]	Mar. 31, 2013 Non-competition agreements [Member] Minimum [Member]	Mar. 31, 2013 Non-competition agreements [Member] Maximum [Member]	Mar. 31, 2013 Site locations [Member]	Dec. 31, 2012 Site locations [Member]	Mar. 31, 2013 Site locations [Member] Maximum [Member]	Mar. 31, 2013 Other [Member]	Dec. 31, 2012 Other [Member]	Mar. 31, 2013 Other [Member] Minimum [Member]	Mar. 31, 2013 Other [Member] Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Life (Years)					7 years	10 years			3 years	15 years			15 years			5 years	15 years
Gross Carrying Amount	$ 2,012,653	$ 2,009,191	$ 483,306	$ 482,883			$ 63,537	$ 63,519			$ 1,451,802	$ 1,449,181		$ 14,008	$ 13,608
Accumulated Amortization	1,567,244	1,540,879	457,559	455,549			62,686	62,566			1,033,595	1,009,631		13,404	13,133
Goodwill gross carrying amount	1,739,342	1,738,686
Goodwill accumulated amortization	$ 253,536	$ 253,536