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Stock-Based Compensation (Tables)
 6 Months Ended
Jun. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of Performance Share Units
The following table summarizes PSUs held by the Company’s officers at June 30, 2013:
 
 
PSUs
 
Weighted Average
Grant Date Fair Value
per Unit
Non-vested PSUs at December 31, 2012
155,220

 
$
26.22

Granted
135,620

 
42.01

Vested
—

 
—

Forfeited
(10,770
)
 
32.89

Non-vested PSUs at June 30, 2013
280,070

 
$
33.61
Summary of Assumptions
The following assumptions were used for the Monte Carlo models to determine the grant date fair value and associated stock-based compensation expense of the PSUs granted:
 
 
2013 Grants
 
2012 Grants
Forecast period (years)
4.00

 
4.01

Risk-free rate
0.65
%
 
0.46
%
Oasis volatility
47.48
%
 
51.00
%