Segment Reporting - Net Sales and Operating Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales									$ 170,761	$ 160,088	$ 176,122
Operating income (loss)	$ (1,877)	$ (920)	$ (1,187)	$ (3,180)	$ (1,125)	$ (1,801)	$ (1,368)	$ (4,470)	(7,164)	(8,764)	(1,322)
Net interest and other expense									(503)	(1,174)	(648)
Loss before income tax expense									(7,667)	(9,938)	(1,970)
Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)									9,080	7,890	15,313
Operating Segments | Mobile Connectivity
Segment Reporting Information [Line Items]
Net sales									133,658	132,227	141,507
Operating income (loss)									4,163	7,334	10,041
Operating Segments | Intertial Navigation
Segment Reporting Information [Line Items]
Net sales									37,103	27,861	34,615
Operating income (loss)									4,917	556	5,272
Unallocated, net
Segment Reporting Information [Line Items]
Operating income (loss)									$ (16,244)	$ (16,654)	$ (16,635)