Mergers and Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Jul. 02, 2018
Assets acquired
Goodwill	$ 159.6	$ 157.0
Hawaiian Telcom Holdco, Inc. [Member]
Assets acquired
Cash			$ 4.3
Receivables			24.8
Inventory, materials and supplies			6.7
Prepaid expenses and other current assets			5.9
Property, plant and equipment			697.6
Goodwill			10.2
Intangible assets			52.0
Deferred income tax asset			45.6
Other noncurrent assets			2.1
Total assets acquired			849.2
Liabilities assumed
Accounts payable			60.0
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			30.8
Total liabilities assumed			509.7
Net assets acquired			$ 339.5