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Stock-Based Compensation - Summary of Unrecognized Compensation Expense - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Unrecognized compensation expense $ 115.8us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Unrecognized compensation expense, weighted-average period (in years) 6 years 1 month 6 days