Segment Data (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | segment	2
Number of reportable segments | segment	2
Site leasing	$ 1,623,173	$ 1,538,070	$ 1,480,634
Total assets	7,320,205	7,360,945
International Site Leasing [Member]
Segment Reporting Information [Line Items]
Total assets	2,028,479	1,839,703
Brazil [Member]
Segment Reporting Information [Line Items]
Site leasing	217,400	178,300	169,600
Total assets	$ 1,278,900	$ 1,096,400	$ 923,600