Revenue from Contracts with Customers - Revenue by Service Offering (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contracts with Customers
Other revenue	$ 31.4	$ 34.7	$ 39.2
Total revenue	725.7	730.2	727.0
Subscription services
Revenue from Contracts with Customers
Revenue	672.0	672.1	663.2
Other business services
Revenue from Contracts with Customers
Revenue	22.3	23.4	24.6
Other business services - Wholesale and colocation lease revenue
Revenue from Contracts with Customers
Revenue	19.4	19.4	18.8
Residential Subscription | Subscription services
Revenue from Contracts with Customers
Revenue	561.6	566.5	562.5
Residential Subscription | HSD
Revenue from Contracts with Customers
Revenue	329.0	294.5	270.3
Residential Subscription | Video
Revenue from Contracts with Customers
Revenue	204.1	236.4	251.2
Residential Subscription | Telephony
Revenue from Contracts with Customers
Revenue	28.5	35.6	41.0
Business Subscription | Subscription services
Revenue from Contracts with Customers
Revenue	110.4	105.6	100.7
Business Subscription | HSD
Revenue from Contracts with Customers
Revenue	70.1	64.5	59.0
Business Subscription | Video
Revenue from Contracts with Customers
Revenue	11.4	11.4	11.0
Business Subscription | Telephony
Revenue from Contracts with Customers
Revenue	$ 28.9	$ 29.7	$ 30.7