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Asset Sales (Details) - USD ($) $ in Millions			3 Months Ended	6 Months Ended
Asset Sales (Details) - USD ($) $ in Millions	Aug. 01, 2017	Jan. 12, 2017	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2018
Asset Sales
Net proceeds from sale of assets				$ 213.0
Gain on sale of assets			$ (0.3)	$ 38.4
Chicago Fiber Network \| Disposal Group, Held-for-sale, Not Discontinued Operations
Asset Sales
Total assets					$ 20.7
Verizon \| Chicago Fiber Network \| Disposal Group Disposed of by Sale, Not Discontinued Operations
Asset Sales
Net proceeds from sale of assets	$ 225.0
Agreement amount for build-out of network	$ 50.0
MidCo \| Lawrence, Kansas System \| Disposal Group Disposed of by Sale, Not Discontinued Operations
Asset Sales
Net proceeds from sale of assets		$ 213.0
Gain on sale of assets		$ 38.4
Period of time in which results are included in financial statements				12 days