Note 11 - Business Segment Information - Revenue by Business Segment Sector (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Revenue	[1]	$ 107,712	$ 106,795
Commercial [Member]
Revenue		$ 62,330	$ 59,682
Revenue, percentage		58.00%	56.00%
Government & Defense [Member]
Revenue		$ 45,382	$ 47,113
Revenue, percentage		42.00%	44.00%
Battery & Energy Products Segment [Member]
Revenue	[1]	$ 91,907	$ 83,996
Battery & Energy Products Segment [Member] | Commercial [Member]
Revenue		62,330	59,682
Battery & Energy Products Segment [Member] | Government & Defense [Member]
Revenue		29,577	24,314
Communications Systems Segment [Member]
Revenue	[1]	15,805	22,799
Communications Systems Segment [Member] | Commercial [Member]
Revenue		0	0
Communications Systems Segment [Member] | Government & Defense [Member]
Revenue		$ 15,805	$ 22,799

[1] Sales classified to U.S. include shipments to U.S.-based prime contractors which in some cases may serve non-U.S. projects.