Acquisitions (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2017 USD ($) item	Mar. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Potential obligation recorded in accrued expenses		$ 8.6	$ 5.8
Other Acquisitions [Member]
Business Acquisition [Line Items]
Number of towers acquired | item		90
Cash paid for acquisition		$ 31.1
Property and equipment		12.1
Intangible assets		17.6
Working capital adjustments		$ 1.4
Subsequent Event [Member]
Business Acquisition [Line Items]
Number of towers acquired | item	9
Cash paid for acquisition	$ 5.6