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Employee Benefit Plans (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]      
Expenses related to employer contributions $ 1.5 $ 1.3 $ 1.3
Expenses related to deferred compensation plan 0.4 0.3 0.4
Deferred compensation liability $ 15.5 $ 12.5  
Nonqualified Deferred Compensation Plan [Member]
      
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]      
Deferred compensation plan, description We provide a 50% match on the first 6% of employee compensation deferred under the Plan, with a maximum match equivalent to 3% of base salary.    
Percent match by employer 50.00%    
Percent of employee's compensation employer will match 6.00%    
Maximum percent of compensation employer will match 3.00%    
Supplemental Deferred Compensation Plan [Member]
      
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]      
Deferred compensation plan, description This plan provides a 50% match on the first 10% of employee compensation deferred under the Plan, with a maximum match equivalent to 5% of compensation.    
Percent match by employer 50.00%    
Percent of employee's compensation employer will match 10.00%    
Maximum percent of compensation employer will match 5.00%