Note 8 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Property, plant and equipment, gross		$ 1,357,929	$ 1,349,899
Less: accumulated depreciation and amortization		(991,816)	(983,050)
Property, plant and equipment, net of accumulated depreciation of $211 and $112		$ 366,113	366,849
Minimum [Member]
Property, plant and equipment, useful lives (Year)		3 years
Maximum [Member]
Property, plant and equipment, useful lives (Year)		50 years
Land, Buildings and Support Assets [Member]
Property, plant and equipment, gross	[1]	$ 195,063	197,999
Less: accumulated depreciation and amortization		$ 0	0
Land, Buildings and Support Assets [Member] | Minimum [Member]
Property, plant and equipment, useful lives (Year)	[1]	5 years
Land, Buildings and Support Assets [Member] | Maximum [Member]
Property, plant and equipment, useful lives (Year)	[1]	42 years
Central Office Switching and Transmission [Member]
Property, plant and equipment, gross		$ 380,954	383,809
Central Office Switching and Transmission [Member] | Minimum [Member]
Property, plant and equipment, useful lives (Year)		5 years
Central Office Switching and Transmission [Member] | Maximum [Member]
Property, plant and equipment, useful lives (Year)		12 years
Outside Plant Cable and Wire Facilities [Member]
Property, plant and equipment, gross		$ 739,547	734,786
Outside Plant Cable and Wire Facilities [Member] | Minimum [Member]
Property, plant and equipment, useful lives (Year)		20 years
Outside Plant Cable and Wire Facilities [Member] | Maximum [Member]
Property, plant and equipment, useful lives (Year)		50 years
Other [Member]
Property, plant and equipment, gross		$ 12,016	7,101
Other [Member] | Minimum [Member]
Property, plant and equipment, useful lives (Year)		3 years
Other [Member] | Maximum [Member]
Property, plant and equipment, useful lives (Year)		5 years
Construction in Progress [Member]
Property, plant and equipment, gross		$ 30,349	$ 26,204

[1] No depreciation charges are recorded for land.