Organization and Basis of Presentation - Discontinued Operations, Assets and Liabilities (Details) $ in Millions	Dec. 31, 2020 USD ($)
Assets
Total current assets	$ 39.2
Current liabilities
Total current liabilities	47.9
Atlantic and Astound broadband markets | Discontinued Operations, Held-for-sale
Assets
Accounts receivable-trade, net of allowance for doubtful accounts of $1.1 and $1.8, respectively	25.1
Accounts receivable-other, net	0.9
Prepaid expenses and other	13.2
Total current assets	39.2
Right-of-use lease assets-operating	2.8
Property, plant and equipment, net	379.4
Franchise operating rights	165.4
Goodwill	183.7
Intangible assets subject to amortization, net	0.2
Other non-current assets	8.5
Total assets	779.2
Current liabilities
Accounts payable-trade	11.4
Current portion of long-term lease liability-operating	0.7
Accrued liabilities and other	18.9
Current portion of unearned service revenue	16.9
Total current liabilities	47.9
Long-term lease liability-operating	2.3
Total liabilities	50.2
Accounts receivable-trade, - Allowance for doubtful accounts	$ 1.8