Mergers and Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2018	Jul. 02, 2018	Dec. 31, 2017	Oct. 02, 2017
Business Acquisition [Line Items]
Goodwill, Purchase Accounting Adjustments		$ 0.7
Assets acquired
Property, plant, and equipment			$ 701.8
Goodwill		$ 158.0		$ 151.0
Hawaiian Telcom Holdco, Inc. [Member]
Assets acquired
Cash			4.3
Receivables			25.7
Inventory, materials and supplies			6.9
Prepaid expenses and other current assets			5.9
Property, plant, and equipment			701.8
Goodwill			7.6
Intangible assets			52.0
Deferred income tax asset			44.3
Other noncurrent assets			2.1
Total assets acquired			850.6
Liabilities assumed
Accounts payable			58.0
Current portion of long-term debt			10.2
Unearned revenue and customer deposits			13.5
Accrued expenses and other current liabilities			21.6
Deferred income tax liabilities			0.0
Long-term debt, less current portion			304.5
Pension and postretirement benefit obligations			68.9
Other noncurrent liabilities			34.4
Total liabilities assumed			511.1
Net assets acquired			$ 339.5
OnX Holdings LLC [Member]
Business Acquisition [Line Items]
Goodwill, Purchase Accounting Adjustments	$ 0.2
Purchase Price Allocation Adjustment, Tax Related	0.1
Purchase Price Allocation Adjustment, Working Capital Related	$ 0.4
Business Acquisition, Goodwill, Expected Tax Deductible Amount					$ 2.3
Assets acquired
Cash					6.5
Receivables					69.9
Inventory, materials and supplies					9.0
Prepaid expenses and other current assets					2.8
Property, plant, and equipment					11.6
Goodwill					133.1
Intangible assets					134.0
Deferred income tax asset					1.4
Other noncurrent assets					1.8
Total assets acquired					370.1
Liabilities assumed
Accounts payable					63.6
Current portion of long-term debt					1.3
Unearned revenue and customer deposits					0.0
Accrued expenses and other current liabilities					18.3
Deferred income tax liabilities					42.3
Long-term debt, less current portion					76.7
Pension and postretirement benefit obligations					0.0
Other noncurrent liabilities					1.5
Total liabilities assumed					203.7
Net assets acquired					$ 166.4