Note 9 - Details of Selected Balance Sheet Accounts - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Property, plant, equipment and seismic rental equipment, gross		$ 172,522	$ 172,086
Less: accumulated depreciation		126,906	126,022
Less: impairment of long-lived assets		36,553	36,553
Property, plant, equipment and seismic rental equipment, net		9,063	9,511
Building [Member]
Property, plant, equipment and seismic rental equipment, gross		15,675	15,675
Machinery and Equipment [Member]
Property, plant, equipment and seismic rental equipment, gross		120,979	120,949
Seismic Rental Equipment [Member]
Property, plant, equipment and seismic rental equipment, gross		2,030	2,003
Furniture and Fixtures [Member]
Property, plant, equipment and seismic rental equipment, gross		3,172	3,172
Property, Plant and Equipment, Other Types [Member]
Property, plant, equipment and seismic rental equipment, gross	[1]	$ 30,666	$ 30,287

[1] Consists primarily of cable-based ocean bottom acquisition technologies that were fully impaired.