Revenue, Deferred Revenue and Deferred Commissions - Schedule of Revenue (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
Disaggregation of Revenue [Line Items]
Revenues	$ 43,256	$ 42,476	$ 40,628	$ 43,114	$ 43,770	$ 43,636	$ 42,325	$ 41,444	$ 169,474	$ 171,175	$ 179,561
Wireless products and services
Disaggregation of Revenue [Line Items]
Revenues									94,277	101,188	109,590
License
Disaggregation of Revenue [Line Items]
Revenues									13,042	9,541	8,832
Professional services
Disaggregation of Revenue [Line Items]
Revenues									18,091	17,630	18,594
Equipment
Disaggregation of Revenue [Line Items]
Revenues									4,995	4,147	5,472
Maintenance
Disaggregation of Revenue [Line Items]
Revenues									39,069	38,669	37,073
United States
Disaggregation of Revenue [Line Items]
Revenues									164,558	166,790	173,852
International
Disaggregation of Revenue [Line Items]
Revenues									$ 4,916	$ 4,385	$ 5,709