Note 3 - Joint Venture - Certain Financial Information About the Joint Venture Included On the Company's Consolidated Balance Sheet (Details) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Property, plant and equipment, accumulated depreciation	$ 1,049,102	$ 1,042,546
ACS Cable Systems LLC and Quintillion Holdings, LLC Joint Venture [Member]
Property, plant and equipment, accumulated depreciation	$ 433		$ 408

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.14)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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