Note 8 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Property, plant and equipment, gross		$ 1,424,904	$ 1,390,622
Less: accumulated depreciation and amortization		(1,042,546)	(1,017,442)
Property, plant and equipment, net of accumulated depreciation of $408 and $309		$ 382,358	373,180
Minimum [Member]
Property, plant and equipment, useful live (Year)		5 years
Maximum [Member]
Property, plant and equipment, useful live (Year)		50 years
Land, Buildings and Support Assets [Member]
Property, plant and equipment, gross	[1]	$ 204,834	197,381
Land, Buildings and Support Assets [Member] | Minimum [Member]
Property, plant and equipment, useful live (Year)	[1]	5 years
Land, Buildings and Support Assets [Member] | Maximum [Member]
Property, plant and equipment, useful live (Year)	[1]	42 years
Central Office Switching and Transmission [Member]
Property, plant and equipment, gross		$ 396,565	387,008
Central Office Switching and Transmission [Member] | Minimum [Member]
Property, plant and equipment, useful live (Year)		5 years
Central Office Switching and Transmission [Member] | Maximum [Member]
Property, plant and equipment, useful live (Year)		12 years
Outside Plant Cable and Wire Facilities [Member]
Property, plant and equipment, gross		$ 765,640	750,492
Outside Plant Cable and Wire Facilities [Member] | Minimum [Member]
Property, plant and equipment, useful live (Year)		10 years
Outside Plant Cable and Wire Facilities [Member] | Maximum [Member]
Property, plant and equipment, useful live (Year)		50 years
Other [Member]
Property, plant and equipment, gross		$ 25,423	17,126
Property, plant and equipment, useful live (Year)		5 years
Construction in Progress [Member]
Property, plant and equipment, gross		$ 32,442	$ 38,615

[1] Depreciation charges are not recorded for land.