Segment information (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2016 USD ($) Segment	Jan. 02, 2016 USD ($)	Sep. 30, 2016 USD ($)
Segment information [Abstract]
Number of reportable segments | Segment	3
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	$ 12,543	$ 9,115
Operating income (loss)	(2,419)	180
Identifiable assets, excluding goodwill	57,212	33,142
Goodwill	7,631	1,435	$ 7,794
Reportable Segments [Member] | Controls [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	7,135	8,707
Operating income (loss)	(2,050)	484
Identifiable assets, excluding goodwill	27,361	32,099
Goodwill	1,435	1,435
Reportable Segments [Member] | Capacitors [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	247	408
Operating income (loss)	(61)	(43)
Identifiable assets, excluding goodwill	796	889
Goodwill	0	0
Reportable Segments [Member] | Chargers [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	5,161	0
Operating income (loss)	(15)	0
Identifiable assets, excluding goodwill	20,399	0
Goodwill	6,196	0
Corporate [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	0	0
Operating income (loss)	(293)	(261)
Identifiable assets, excluding goodwill	8,656	154
Goodwill	$ 0	$ 0