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Equity-Based Compensation (CPE Inc. only) (Details 2) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based compensation plans      
Recognized compensation expense $ 11,796,000 $ 8,796,000 $ 7,234,000
Total ESPP compensation expense 11,796,000 8,796,000 7,234,000
Employee stock purchase plan
     
Share-based compensation plans      
Maximum number of shares reserved for sale (in shares) 500,000    
Minimum term of service for eligibility 6 months    
Minimum hours of service completed per calendar year for eligibility 1000 hours    
Maximum contribution of eligible earnings by participating employees per pay period 200    
Maximum contribution of eligible earnings by participating employees per plan year 4,800    
Percentage of purchase price of common stock purchased under ESPP to fair market value of common stock on offering date 90.00%    
Percentage of purchase price of common stock purchased under ESPP to fair market value of common stock on last day of option period 90.00%    
Unrecognized compensation expense 300,000 300,000  
Recognized compensation expense 100,000 100,000  
Total ESPP compensation expense $ 400,000 $ 400,000  
Assumptions:      
Weighted-average fair value (per award) $ 5.51 $ 6.04  
Risk-free interest rate (as a percent) 0.20% 0.10%  
Expected option life 1 year 1 year  
Expected volatility (as a percent) 44.70% 43.00%