Acquisitions (Narrative) (Detail) (USD $) Share data in Millions, unless otherwise specified	0 Months Ended	3 Months Ended		9 Months Ended
	Apr. 02, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2012
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	5.25
Transaction costs associated with acquisition						13,200,000
Revenues from acquisition				55,400,000
Net loss from acquisition				17,700,000
Tower acquisitions (number of towers)				37
Ground lease extensions		1,200,000	3,300,000	4,700,000	7,200,000
Contingent consideration, income, net		500,000	30,000	1,300,000	100,000
Potential obligation recorded in accrued expenses				$ 9,200,000