Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 1,498,691		$ 1,403,118
Less: accumulated amortization and depreciation	798,577		701,759
Property, plant and equipment, net	700,114	$ 703,148	701,359
Decrease in depreciation	3,000
Land
Property, plant and equipment [Abstract]
Total property, plant and equipment	6,976		6,723
Buildings and structures
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 232,730		213,657
Buildings and structures | Minimum
Property, plant and equipment [Abstract]
Estimated useful lives	10 years
Buildings and structures | Maximum
Property, plant and equipment [Abstract]
Estimated useful lives	40 years
Cable and fiber
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 334,260		309,928
Cable and fiber | Minimum
Property, plant and equipment [Abstract]
Estimated useful lives	15 years
Cable and fiber | Maximum
Property, plant and equipment [Abstract]
Estimated useful lives	40 years
Equipment and software
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 867,898		791,401
Equipment and software | Minimum
Property, plant and equipment [Abstract]
Estimated useful lives	3 years
Equipment and software | Maximum
Property, plant and equipment [Abstract]
Estimated useful lives	20 years
Plant in service
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 1,441,864		1,321,709
Plant under construction
Property, plant and equipment [Abstract]
Total property, plant and equipment	$ 56,827		$ 81,409