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Stock-Based Compensation - Summary of Assumptions (Detail) (Performance Share Unit Awards [Member])
12 Months Ended
Dec. 31, 2012
Performance Share Unit Awards [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Forecast period (years) 4 years 2 days
Risk-free rate 0.46%
Oasis volatility 51.00%