Segment Reporting Net Sales and Operating Earnings (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net sales	$ 39,311	$ 39,312	$ 115,417	$ 113,349
Loss from operations	(4,858)	(1,857)	(17,771)	(8,269)
Net interest and other income (expense)	1,058	(66)	1,532	(372)
Loss from continuing operations before income tax (benefit) expense	(3,800)	(1,923)	(16,239)	(8,641)
Operating Segments
Segment Reporting Information [Line Items]
Loss from operations	(438)	2,426	(4,051)	4,500
Operating Segments | Mobile connectivity
Segment Reporting Information [Line Items]
Net sales	31,642	29,220	92,025	86,277
Loss from operations	(267)	506	(4,075)	682
Operating Segments | Inertial navigation
Segment Reporting Information [Line Items]
Net sales	7,669	10,092	23,392	27,072
Loss from operations	(171)	1,920	24	3,818
Unallocated
Segment Reporting Information [Line Items]
Loss from operations	$ (4,420)	$ (4,283)	$ (13,720)	$ (12,769)