Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, plant and equipment
Property, plant and equipment cost	$ 1,036,137	$ 937,927
Less accumulated depreciation and amortization	440,140	358,820
Total property, plant and equipment, net	595,997	579,107
Depreciation expense	87,800	85,400	$ 75,100
Land
Property, plant and equipment
Property, plant and equipment cost	67,278	67,278
Buildings
Property, plant and equipment
Property, plant and equipment cost	115,775	114,351
Central office equipment
Property, plant and equipment
Property, plant and equipment cost	208,004	194,707
Outside communications plant
Property, plant and equipment
Property, plant and equipment cost	412,244	377,042
Other equipment, vehicles and furniture
Property, plant and equipment
Property, plant and equipment cost	87,849	74,377
Construction in progress
Property, plant and equipment
Property, plant and equipment cost	55,606	32,595
Software
Property, plant and equipment
Property, plant and equipment cost	78,547	66,704
Other property
Property, plant and equipment
Property, plant and equipment cost	$ 10,834	$ 10,873