Acquisitions (Narrative) (Detail) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended
	Apr. 02, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Business Acquisition, Contingent Consideration [Line Items]
Owned towers	2,281
Additional towers in Development	36
Total consideration of acquisition	$ 1,100,000,000
Total consideration paid in cash	850,000,000
Newly issued shares	5,250,000
Class A common stock value	263,300,000			263,340,000
Class A common stock market price	$ 50.16
Transaction costs associated with acquisition		11,400,000		11,400,000
Revenues from acquisition				27,400,000
Net loss from acquisition				11,200,000
Tower acquisitions (number of towers)		100
Ground lease extensions		2,100,000	2,700,000	3,600,000	3,900,000
Contingent consideration, income, net		2,200,000	400,000	800,000	200,000
Potential obligation recorded in accrued expenses				$ 2,500,000