Acquisitions (Narrative) (Details) $ in Millions	1 Months Ended			12 Months Ended
	Jan. 31, 2019 USD ($) item	Dec. 31, 2017 USD ($) item	Nov. 30, 2014 item	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) item
Business Acquisition [Line Items]
Number of towers acquired | item		941	1,641	1,316	1,425	531
Cash paid for acquisition						$ 214.7
Property and equipment						72.8
Intangible assets						144.4
Working capital adjustments						$ 2.5
Other Acquisitions [Member]
Business Acquisition [Line Items]
Number of towers acquired | item				1,316	1,425
Property and equipment		$ 114.7		$ 134.5	$ 114.7
Intangible assets		345.3		280.7	345.3
Working capital adjustments		$ 3.8		$ 8.5	$ 3.8
Subsequent Event [Member]
Business Acquisition [Line Items]
Number of towers acquired | item	27
Cash paid for acquisition	$ 10.7