Long-Term Payment Obligation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2012
Related Party Transaction [Line Items]
Interest accreted on long-term payment obligation	$ 0.1	$ 0.1	$ 0.3	$ 0.3
Secure Keyboards Ltd
Related Party Transaction [Line Items]
Percentage of ownership by a related party following acquisition			24.50%		30.00%
Secure Networks Ltd
Related Party Transaction [Line Items]
Percentage of ownership by a related party following acquisition					9.00%
Settlement Agreement | Maximum
Related Party Transaction [Line Items]
Installment payment, contractual payment year			2020