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, 2018	Dec. 31, 2017	Dec. 31, 2016
AT&T [Member]
Concentration Risk [Line Items]
Concentration risk percentage	24.00%	25.00%	25.70%
Sprint [Member]
Concentration Risk [Line Items]
Concentration risk percentage	17.90%	15.10%	16.10%
T-Mobile [Member]
Concentration Risk [Line Items]
Concentration risk percentage	16.40%	16.50%	17.00%
Verizon Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage	14.70%	15.20%	15.20%
Domestic Site Leasing [Member] | AT&T [Member]
Concentration Risk [Line Items]
Concentration risk percentage	31.90%	32.70%	32.70%
Domestic Site Leasing [Member] | Sprint [Member]
Concentration Risk [Line Items]
Concentration risk percentage	19.60%	18.90%	19.80%
Domestic Site Leasing [Member] | T-Mobile [Member]
Concentration Risk [Line Items]
Concentration risk percentage	20.30%	19.70%	19.60%
Domestic Site Leasing [Member] | Verizon Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage	19.00%	19.00%	18.20%
International Site Leasing [Member] | Oi S.A. [Member]
Concentration Risk [Line Items]
Concentration risk percentage	35.50%	42.20%	43.90%
International Site Leasing [Member] | Telefonica [Member]
Concentration Risk [Line Items]
Concentration risk percentage	26.70%	25.70%	26.40%
International Site Leasing [Member] | Claro [Member]
Concentration Risk [Line Items]
Concentration risk percentage	11.40%	10.00%	9.40%
Site Development [Member]
Concentration Risk [Line Items]
Concentration risk percentage	7.00%
Site Development [Member] | Sprint [Member]
Concentration Risk [Line Items]
Concentration risk percentage	47.10%	12.90%	11.70%
Site Development [Member] | T-Mobile [Member]
Concentration Risk [Line Items]
Concentration risk percentage	16.40%	26.90%	28.40%
Site Development [Member] | Verizon Wireless [Member]
Concentration Risk [Line Items]
Concentration risk percentage	6.40%	12.80%	16.50%
Site Development [Member] | Nokia, Inc. [Member]
Concentration Risk [Line Items]
Concentration risk percentage	3.20%	10.10%	7.10%