Earnings Per Common Share (Schedule of Earnings Per Basic And Diluted by Common Class) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Common Share
Income from continuing operations attributable to American Tower Corporation (in dollars)	$ 637,283	$ 396,462	$ 372,906
Basic weighted average common shares outstanding	394,772	395,711	401,152
Dilutive securities	4,515	4,484	2,920
Diluted weighted average common shares outstanding	399,287	400,195	404,072
Basic income from continuing operations attributable to American Tower Corporation per common share (in dollars per share)	$ 1.61	$ 1.00	$ 0.93
Diluted income from continuing operations attributable to American Tower Corporation per common share (in dollars per share)	$ 1.60	$ 0.99	$ 0.92