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Stock-based Compensation - Vested RSUs - Additional Information (Detail)
$ in Millions
9 Months Ended
Sep. 30, 2015
USD ($)
shares
RSUs [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Fair value of RSUs vested during the year | $ $ 27.5
Aggregate intrinsic value of RSUs vested and expected to vest | $ $ 68.0
Weighted average period of recognition of unrecognized compensation cost 1 year 3 months 18 days
Performance-based Stock Options [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Options granted 0
Market-based Stock Options [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Options granted 0