Segment Reporting - Net Sales and Operating Earnings (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net sales	$ 36,568	$ 36,376
Operating (loss) income	(7,648)	(6,234)
Net interest and other income (expense)	1,811	(307)
Loss from continuing operations before income tax expense (benefit)	(5,837)	(6,541)
Operating Segments
Segment Reporting Information [Line Items]
Operating (loss) income	(3,120)	(1,001)
Operating Segments | Mobile Connectivity
Segment Reporting Information [Line Items]
Net sales	28,896	28,914
Operating (loss) income	(2,299)	(1,444)
Operating Segments | Intertial Navigation
Segment Reporting Information [Line Items]
Net sales	7,672	7,462
Operating (loss) income	(821)	443
Segment Reconciling Items
Segment Reporting Information [Line Items]
Operating (loss) income	$ (4,528)	$ (5,233)