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Stock-based Compensation - Valuation Assumptions - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Grant date fair value of RSUs vested $ 6.2
Aggregate intrinsic value of Restricted Stock Units expected to vest $ 51.2
Remaining weighted average vesting period, in years 10 months 24 days