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Capital Lease and Financing Arrangements - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2012
Aug. 01, 2011
Year
Debt Instrument [Line Items]      
Outstanding letters of credit $ 2.6 $ 2.6  
Unused and available borrowings under bank revolving line of credit 47.4 47.4  
Number of chassis leased     3,126
Chassis, lease agreement period (years)     10
Capital lease, interest paid $ 0.2 $ 0.5  
Beginning
     
Debt Instrument [Line Items]      
Letters of credit expiration, year   2012  
Ending
     
Debt Instrument [Line Items]      
Letters of credit expiration, year   2013