Revenue from Contracts with Customers (ASC 606) - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from External Customer [Line Items]
Total net sales	$ 170,761	$ 160,088	$ 176,122
Product
Revenue from External Customer [Line Items]
Total net sales	63,277	56,968	73,075
Service
Revenue from External Customer [Line Items]
Total net sales	107,484	$ 103,120	$ 103,047
Mobile Connectivity | Service
Revenue from External Customer [Line Items]
Total net sales	102,307
Intertial Navigation | Product
Revenue from External Customer [Line Items]
Total net sales	31,926
Intertial Navigation | Service
Revenue from External Customer [Line Items]
Total net sales	5,177
Transferred at point in time | Mobile Connectivity | Product
Revenue from External Customer [Line Items]
Total net sales	26,086
Transferred over time | Mobile Connectivity | Product
Revenue from External Customer [Line Items]
Total net sales	$ 5,265