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Equity Incentive Compensation Plans (Restricted Stock Units and Performance Share Program Parenthetical) (Details) (USD $)
1 Months Ended 12 Months Ended
Mar. 31, 2011
ratio
performancefactor
simulation
Mar. 31, 2010
simulation
Dec. 31, 2011
performancefactor
year
Dec. 31, 2010
Dec. 31, 2009
Equity Incentive Compensation Plans          
Total unrecognized compensation cost     $ 1,300,000    
Period of recognition of unrecognized compensation cost (in years)     3.25    
Vesting period (in years)     4 years    
Fair value assumptions used in market-based portion of performance shares valuation model (Monte Carlo model)          
Expected volatility (as a percent)     45.00%    
Risk-free interest rate (as a percent)     2.54%    
Restricted Stock Units
         
Equity Incentive Compensation Plans          
Total unrecognized compensation cost     7,900,000    
Period of recognition of unrecognized compensation cost (in years)     3.25    
Granted (in shares)     159,333 34,529 294,504
Restricted Stock Units | Executive officers and other officers
         
Equity Incentive Compensation Plans          
Fully Vested Shares Outstanding Subject to Deferral Election by Executive Officers or Other Officers (in shares)     483,908 289,335 124,799
Restricted Stock Units | Non-employee directors
         
Equity Incentive Compensation Plans          
Percentage of stock units vested at date of grant (as a percent)     100.00%    
Fully Vested Shares Outstanding Subject to Non-Employee Director Deferral Election (in shares)     30,544 10,522 10,522
Performance-Based RSUs
         
Equity Incentive Compensation Plans          
Total unrecognized compensation cost     1,400,000    
Period of recognition of unrecognized compensation cost (in years)     2    
Granted (in shares)     65,620 103,794 0
Number of years of service to be completed to participate in the program (in years) 3 years        
Minimum interest coverage ratio, numerator 2.5        
Minimum interest coverage ratio, denominator 1.0        
Number of equally weighted performance factors 2   2    
Vesting period (in years) 3 years   3 years    
Grant date fair value determined by Monte Carlo valuation model $ 1,100,000 $ 1,000,000      
Fair value assumptions used in market-based portion of performance shares valuation model (Monte Carlo model)          
Number of simulations 100,000 100,000      
Expected volatility (as a percent) 44.00% 79.00%      
Risk-free interest rate (as a percent) 1.15% 1.36%      
Performance-Based RSUs | Executive officers and other officers
         
Equity Incentive Compensation Plans          
Granted (in shares) 65,620