Quarterly report pursuant to Section 13 or 15(d)

Stock-based Compensation Plans and Awards - Schedule of assumptions used for determining the per-share fair value (Details)

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Stock-based Compensation Plans and Awards - Schedule of assumptions used for determining the per-share fair value (Details) - Employee stock - Black Scholes Options Pricing Model
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Assumptions used to calculate per-share fair value of award        
Expected life (in years) 6 months 6 months 6 months 6 months
Risk-free interest rate 0.07% 0.08%   0.08%
Expected volatility 42.00% 42.00% 42.00% 42.00%
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Minimum        
Assumptions used to calculate per-share fair value of award        
Risk-free interest rate     0.05%  
Maximum        
Assumptions used to calculate per-share fair value of award        
Risk-free interest rate     0.07%