Concentration Of Credit Risk (Summary Of Significant Customers And Percentage Of Total Revenue For Specified Time Periods Derived From Such Customers) (Details) - Revenue [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AT&T Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	25.70%	24.20%	23.00%
T-Mobile [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	17.00%	16.00%	15.50%
Sprint [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	16.10%	19.60%	23.40%
Verizon Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	15.20%	13.80%	12.00%
Domestic Site Leasing [Member] | AT&T Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	32.70%	31.90%	30.10%
Domestic Site Leasing [Member] | T-Mobile [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	19.60%	19.00%	19.20%
Domestic Site Leasing [Member] | Sprint [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	19.80%	22.30%	25.60%
Domestic Site Leasing [Member] | Verizon Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	18.20%	16.30%	14.40%
International Site Leasing [Member] | Oi S.A. [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	43.90%	48.80%	44.30%
International Site Leasing [Member] | Telefonica [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	26.40%	24.70%	28.80%
Site Development Revenue [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	6.00%
Site Development Revenue [Member] | T-Mobile [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	28.40%	17.60%	8.50%
Site Development Revenue [Member] | Sprint [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	11.70%	28.50%	36.70%
Site Development Revenue [Member] | Verizon Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	16.50%	14.80%	10.10%
Site Development Revenue [Member] | Ericsson, Inc [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue	5.00%	15.30%	16.80%