Note 12 - Business Segment Information - Domestic and International Revenue by Segment (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Revenues	[1]	$ 25,814	$ 18,882
Revenue, percentage	[1]
UNITED STATES
Revenues	[1]	$ 15,638	$ 10,021
Revenue, percentage	[1]	61.00%	53.00%
Non-US [Member]
Revenues	[1]	$ 10,176	$ 8,861
Revenue, percentage	[1]	39.00%	47.00%
Battery & Energy Products Segment [Member]
Revenues	[1]	$ 20,761	$ 15,998
Battery & Energy Products Segment [Member] | UNITED STATES
Revenues	[1]	11,284	7,567
Battery & Energy Products Segment [Member] | Non-US [Member]
Revenues	[1]	9,477	8,431
Communications Systems Segment [Member]
Revenues	[1]	5,053	2,884
Communications Systems Segment [Member] | UNITED STATES
Revenues	[1]	4,354	2,454
Communications Systems Segment [Member] | Non-US [Member]
Revenues	[1]	$ 699	$ 430

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