Acquisitions (Narrative) (Details) $ in Millions				3 Months Ended
	May 01, 2017 USD ($) ft² MW	Mar. 01, 2017 USD ($) building item mi Center	Oct. 03, 2016 USD ($) ft² item MW	Sep. 30, 2017 USD ($) item	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Number of business combinations completed | item				41
Acquisition related costs				$ 8.3	$ 3.0
KIO Networks US Data Centers
Business Acquisition [Line Items]
Business acquisition purchase price	$ 11.9
Acquired facility size (in square feet) | ft²	100,000
Acquired megawatts of critical power | MW	2
Purchase price, held in escrow	$ 1.2
Electric Lightwave
Business Acquisition [Line Items]
Business acquisition purchase price		$ 1,426.6
Purchase price, held in escrow		$ 7.0
Number of metropolitan markets | item		35
Remaining cash consideration to be paid		$ 0.2
Number of on-net buildings connected | building		3,100
Number of data centers | Center		100
Electric Lightwave | Long Haul Fiber [Member]
Business Acquisition [Line Items]
Additional Route Miles Acquired | mi		8,100
Electric Lightwave | Metro Fiber [Member]
Business Acquisition [Line Items]
Additional Route Miles Acquired | mi		4,000
Santa Clara Data Center
Business Acquisition [Line Items]
Business acquisition purchase price			$ 11.3
Acquired facility size (in square feet) | ft²			26,900
Acquired megawatts of critical power | MW			3
Remaining cash consideration to be paid			$ 7.7
Number of quarterly payments | item			10
Amount of quarterly payments			$ 1.3