Property, Plant and Equipment, Net - Components (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment, Net
Total property, plant and equipment	$ 1,988.2		$ 1,988.2		$ 1,889.1
Less accumulated depreciation	(1,269.4)		(1,269.4)		(1,168.2)
Plant, Property and Equipment, Net	718.8		718.8		720.9
Depreciation expense	42.2	$ 38.0	125.7	$ 110.7
Distribution facilities
Property, Plant and Equipment, Net
Total property, plant and equipment	1,216.2		1,216.2		1,148.8
Customer premise equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	264.0		264.0		266.2
Head-end equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	220.0		220.0		209.5
Telephony infrastructure
Property, Plant and Equipment, Net
Total property, plant and equipment	52.3		52.3		52.5
Computer equipment and software
Property, Plant and Equipment, Net
Total property, plant and equipment	119.4		119.4		102.5
Vehicles
Property, Plant and Equipment, Net
Total property, plant and equipment	23.1		23.1		22.7
Buildings and leasehold improvements
Property, Plant and Equipment, Net
Total property, plant and equipment	32.0		32.0		31.0
Office and technical equipment
Property, Plant and Equipment, Net
Total property, plant and equipment	18.7		18.7		18.7
Land
Property, Plant and Equipment, Net
Total property, plant and equipment	4.4		4.4		4.4
Construction in progress (including material inventory and other)
Property, Plant and Equipment, Net
Total property, plant and equipment	$ 38.1		$ 38.1		$ 32.8