Mergers and Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Jul. 02, 2018
Assets acquired
Goodwill	$ 158.6	$ 157.0
Hawaiian Telcom Holdco, Inc. [Member]
Assets acquired
Cash			$ 4.3
Receivables			25.5
Inventory, materials and supplies			6.9
Prepaid expenses and other current assets			5.9
Property, plant and equipment			701.5
Goodwill			9.6
Intangible assets			52.0
Deferred income tax asset			43.8
Other noncurrent assets			2.1
Total assets acquired			851.6
Liabilities assumed
Accounts payable			59.2
Current portion of long-term debt			10.2
Unearned revenue and customer deposits			13.5
Accrued expenses and other current liabilities			21.8
Long-term debt, less current portion			304.5
Pension and postretirement benefit obligations			68.9
Other noncurrent liabilities			34.0
Total liabilities assumed			512.1
Net assets acquired			$ 339.5