Revenue from Contracts with Customers (ASC 606) - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 39,972	$ 40,101
Product
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	12,874	13,992
Product | Intertial Navigation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	5,812	6,072
Service
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	27,098	26,109
Service | Mobile Connectivity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	25,448	24,829
Service | Intertial Navigation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	1,650	1,280
Transferred at Point in Time | Product | Mobile Connectivity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	5,677	6,670
Transferred over Time | Product | Mobile Connectivity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 1,385	$ 1,250