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Long-Term Debt And Financing Arrangements (Details) (USD $)
In Millions, unless otherwise specified
 0 Months Ended 12 Months Ended
Mar. 31, 2011
Mar. 31, 2011
Dec. 31, 2011
Aug. 01, 2011
Dec. 31, 2010
Interest rate under the credit agreement The interest rate under the Credit Agreement is equal to LIBOR plus 1.75%.        
Current unsecured borrowing capacity $ 10.0 $ 10.0      
Maximum unsecured borrowing capacity 50.0 50.0      
Amount increase over LIBOR to determine interest rate of the credit agreement   1.75%      
Line of credit, expiration date   March 2014      
Letter of credit expiration, year     2012    
Minimum net worth 300.0 300.0      
Commitment fee charged on the unused line of credit   0.375%      
Outstanding letters of credit     2.6    
Unused and available borrowings under bank revolving line of credit     47.4   7.4
Number of chassis leased       3,126  
Chassis, lease agreement period (years)     10    
Capital lease interest paid     $ 0.3    
Maximum [Member]
          
Cash Flow Leverage Ratio   2.0