Operating Segments and Concentrations of Credit Risk (Major Customers) (Details)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Concentration Risk, Percentage	76.00%	74.00%	86.00%
AT&T [Member]
Concentration Risk, Percentage	21.00%	20.00%	25.00%
T-Mobile [Member]
Concentration Risk, Percentage	22.00%	19.00%	22.00%
Verizon Wireless [Member]
Concentration Risk, Percentage	19.00%	20.00%	16.00%
Sprint [Member]
Concentration Risk, Percentage	14.00%	15.00%	23.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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