Note 11 - Business Segment Information - Domestic and International Revenue by Segment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Revenue	[1]	$ 107,712	$ 106,795
UNITED STATES
Revenue	[1]	$ 62,255	$ 63,375
Revenue, percentage	[1]	58.00%	59.00%
Non-US [Member]
Revenue	[1]	$ 45,457	$ 43,420
Revenue, percentage	[1]	42.00%	41.00%
Battery & Energy Products Segment [Member]
Revenue	[1]	$ 91,907	$ 83,996
Battery & Energy Products Segment [Member] | UNITED STATES
Revenue	[1]	49,930	42,224
Battery & Energy Products Segment [Member] | Non-US [Member]
Revenue	[1]	41,977	41,772
Communications Systems Segment [Member]
Revenue	[1]	15,805	22,799
Communications Systems Segment [Member] | UNITED STATES
Revenue	[1]	12,325	21,151
Communications Systems Segment [Member] | Non-US [Member]
Revenue	[1]	$ 3,480	$ 1,648

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