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Stock-Based Compensation (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
item
Dec. 31, 2011
Dec. 31, 2010
Stock-Based Compensation      
Number of stock-based compensation plans 2    
Summary of the activity relating to the options outstanding      
Exercised (in shares) (245,000) (332,000) (146,000)
LTIP | Maximum
      
Stock-Based Compensation      
Maximum grants of awards (in shares) 3,000,000    
Stock Option
      
Stock-Based Compensation      
Exercisable period from date of grant 10 years    
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules      
Risk-free interest rate (as a percent)   2.40% 3.00%
Expected dividend yield (as a percent) 0.00% 0.00% 0.00%
Weighted average expected volatility (as a percent) 50.00% 49.00% 50.00%
Expected term   6 years 6 years
Weighted average grant-date fair value (in dollars per share) 8.57 11.88 8.72
Summary of the activity relating to the options outstanding      
Outstanding at the beginning of the period (in shares) 1,514,884 1,766,253 1,817,332
Granted (in shares) 169,088 90,080 106,912
Exercised (in shares) (245,054) (332,099) (145,715)
Forfeited (in shares) (4,680) (8,850) (12,276)
Expired (in shares) (2,010) (500)  
Outstanding at the end of the period (in shares) 1,432,228 1,514,884 1,766,253
Exercisable at the end of the period (in shares) 1,179,959    
Weighted Average Exercise Price      
Outstanding at the beginning of the period (in dollars per share) 8.82 7.18 6.43
Granted (in dollars per share) 17.76 24.18 17.18
Exercised (in dollars per share) 5.78 4.12 4.60
Forfeited (in dollars per share) 19.19 14.89 13.57
Expired (in dollars per share) 18.85 13.00  
Outstanding at the end of the period (in dollars per share) 10.34 8.82 7.18
Exercisable at the end of the period (in dollars per share) 8.49    
Weighted Average Remaining Contractual Term      
Outstanding at the end of the period 5 years 1 month 6 days 5 years 6 months 6 years 1 month 6 days
Exercisable at the end of the period 4 years 4 months 24 days    
Aggregate Intrinsic Value      
Outstanding at the end of the period (in dollars) 17,220 16,083 24,398
Exercisable at the end of the period (in dollars) 16,305    
Stock Option | Minimum
      
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules      
Vesting period 3 years    
Risk-free interest rate (as a percent) 1.20%    
Expected term 6 years    
Stock Option | Maximum
      
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules      
Vesting period 4 years    
Volatility period over which the entity's common stock was publicly traded 4 years    
Risk-free interest rate (as a percent) 1.40%    
Expected term 6 years 3 months 18 days    
Restricted Stock | Eligible members of the Board of Directors
      
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules      
Vesting period 3 years    
Restricted Stock | Minimum | Various employees
      
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules      
Vesting period 3 years    
Restricted Stock | Maximum | Various employees
      
Assumptions used in determining the fair value of stock options granted for fixed awards with graded vesting schedules      
Vesting period 5 years