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Deferred Revenue - Additional Information (Detail) - USD ($)
$ in Millions
Jun. 30, 2016
Dec. 31, 2015
Jun. 30, 2015
Deferred Revenue Arrangement [Line Items]      
Deferred revenue current liabilities $ 24.0 $ 22.9  
Deferred revenue non-current liabilities 60.3 $ 56.4  
Extended Transmission Coverage      
Deferred Revenue Arrangement [Line Items]      
Deferred revenue current liabilities 24.0   $ 21.9
Deferred revenue non-current liabilities $ 60.3   $ 52.8