Note 4 - Supplemental Balance Sheet Information - Summary of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Goodwill balance	$ 19,965	$ 16,283
Effect of Foreign Currency Translation	493	(805)
Goodwill balance	20,458	19,965
Accutronics Limited [Member]
Acquisition of Accutronics		4,487
Battery & Energy Products Segment [Member]
Goodwill balance	8,472	4,790
Effect of Foreign Currency Translation	493	(805)
Goodwill balance	8,965	8,472
Battery & Energy Products Segment [Member] \| Accutronics Limited [Member]
Acquisition of Accutronics		4,487
Communications Systems Segment [Member]
Goodwill balance	11,493	11,493
Effect of Foreign Currency Translation
Goodwill balance	$ 11,493	11,493
Communications Systems Segment [Member] \| Accutronics Limited [Member]
Acquisition of Accutronics

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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