Segment Reporting Segment Reporting - Net Sales and Operating Earnings (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 39,972	$ 40,101
Operating (loss) income	(5,829)	(3,180)
Net interest and other expense	(316)	(535)
Loss before income tax expense	(6,145)	(3,715)
Operating Segments
Segment Reporting Information [Line Items]
Operating (loss) income	(596)	1,406
Operating Segments | Mobile Connectivity
Segment Reporting Information [Line Items]
Net sales	32,510	32,749
Operating (loss) income	(1,039)	1,072
Operating Segments | Intertial Navigation
Segment Reporting Information [Line Items]
Net sales	7,462	7,352
Operating (loss) income	443	334
Segment Reconciling Items
Segment Reporting Information [Line Items]
Operating (loss) income	$ (5,233)	$ (4,586)