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Stock-Based Awards - Summary of Options Activity (Detail) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Options, beginning balance 12,760,191 20,852,614 21,443,617
Options, granted       825,000
Options, forfeitures or expirations (40,000) (73,907) (135,316)
Options, exercised (4,875,500) (8,018,516) (1,280,687)
Options, ending balance 7,844,691 12,760,191 20,852,614
Weighted average exercise price of options, beginning balance $ 0.95 $ 0.79 $ 0.60
Weighted average exercise price of options, granted $ 0.00 $ 0.00 $ 5.80
Weighted average exercise price of options, forfeitures or expirations $ 4.11 $ 1.75 $ 2.04
Weighted average exercise price of options, exercised $ 0.38 $ 0.58 $ 0.64
Weighted average exercise price of options, ending balance $ 1.29 $ 0.95 $ 0.79