Concentration of Credit Risk (Major Customers) (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Percentage of revenues from tenants accounting for more than 10% of the Company's revenues	90.00%	89.00%	89.00%
Sprint [Member]
Percentage of revenues from tenants accounting for more than 10% of the Company's revenues	33.00%	35.00%	36.00%
AT&T [Member]
Percentage of revenues from tenants accounting for more than 10% of the Company's revenues	22.00%	20.00%	20.00%
T-Mobile [Member]
Percentage of revenues from tenants accounting for more than 10% of the Company's revenues	20.00%	19.00%	19.00%
Verizon Wireless [Member]
Percentage of revenues from tenants accounting for more than 10% of the Company's revenues	15.00%	15.00%	14.00%