Note 11 - Business Segment Information - Revenue by Business Segment Sector (Details) - USD ($) $ in Thousands	3 Months Ended					9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019	Sep. 29, 2019	[1]	Sep. 30, 2020		Sep. 30, 2019	Sep. 29, 2019	[1]
Revenue	$ 24,362	[1]	$ 27,493	$ 27,493		$ 78,736	[1]	$ 75,772	$ 75,772
Commercial [Member]
Revenue	$ 15,772		$ 17,677			$ 46,746		$ 42,736
Revenue, percentage	65.00%		64.00%			59.00%		56.00%
Government & Defense [Member]
Revenue	$ 8,590		$ 9,816			$ 31,990		$ 33,036
Revenue, percentage	35.00%		36.00%			41.00%		44.00%
Battery & Energy Products Segment [Member]
Revenue	$ 21,819	[1]	$ 22,578	22,578		$ 66,616	[1]	$ 58,876	58,876
Battery & Energy Products Segment [Member] | Commercial [Member]
Revenue	15,772		17,677			46,746		42,736
Battery & Energy Products Segment [Member] | Government & Defense [Member]
Revenue	6,047		4,901			19,870		16,140
Communications Systems Segment [Member]
Revenue	2,543	[1]	4,915	$ 4,915		12,120	[1]	16,896	$ 16,896
Communications Systems Segment [Member] | Commercial [Member]
Revenue	0		0			0		0
Communications Systems Segment [Member] | Government & Defense [Member]
Revenue	$ 2,543		$ 4,915			$ 12,120		$ 16,896

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