Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 1,471,159	$ 1,471,159		$ 1,403,118
Less accumulated amortization and depreciation	782,643	782,643		701,759
Property, plant and equipment, net	688,516	688,516	$ 703,148	701,359
Depreciation expense	800	800
Land
Property, plant and equipment [Abstract]
Total property, plant and equipment	6,936	6,936		6,723
Buildings and structures
Property, plant and equipment [Abstract]
Total property, plant and equipment	231,962	231,962		213,657
Cable and fiber
Property, plant and equipment [Abstract]
Total property, plant and equipment	321,963	321,963		309,928
Equipment and software
Property, plant and equipment [Abstract]
Total property, plant and equipment	839,624	839,624		791,401
Plant in service
Property, plant and equipment [Abstract]
Total property, plant and equipment	1,400,485	1,400,485		1,321,709
Plant under construction
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 70,674	$ 70,674		$ 81,409
Minimum | Buildings and structures
Property, Plant and Equipment [Line Items]
Useful life (in years)		10 years
Minimum | Cable and fiber
Property, Plant and Equipment [Line Items]
Useful life (in years)		15 years
Minimum | Equipment and software
Property, Plant and Equipment [Line Items]
Useful life (in years)		3 years
Maximum | Buildings and structures
Property, Plant and Equipment [Line Items]
Useful life (in years)		40 years
Maximum | Cable and fiber
Property, Plant and Equipment [Line Items]
Useful life (in years)		40 years
Maximum | Equipment and software
Property, Plant and Equipment [Line Items]
Useful life (in years)		20 years