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Revolving Credit Facility - Additional Information (Detail) (USD $)
 9 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Line of Credit Facility [Line Items]    
Line of credit facility expiration date Oct. 01, 2017  
Revolving credit facility borrowing capacity $ 24,000,000  
Letters of credit outstanding amount 70,600,000  
Restricted certificates of deposit related to California workers' compensation 63,944,000 0
Interest calculation under revolving credit facility The Agreement also provides for an unused commitment fee of 0.25% per annum on the average daily unused amount of the revolving credit facility  
Ratio of restricted and unrestricted cash and marketable securities to workers' compensation and safety incentive liabilities 1.0  
Prohibition on incurring additional indebtedness without the prior approval of the Bank in purchase money financing 200,000  
September 30, 2014 [Member]
    
Line of Credit Facility [Line Items]    
Funded debt to EBITDA ratio 1.75  
September 30, 2015 [Member]
    
Line of Credit Facility [Line Items]    
Funded debt to EBITDA ratio 1.5  
Thereafter [Member]
    
Line of Credit Facility [Line Items]    
Funded debt to EBITDA ratio 1.25  
Revolving Credit Facility [Member]
    
Line of Credit Facility [Line Items]    
Outstanding borrowings on the revolving credit facility 0  
LIBOR plus rate 1.75%  
Unused commitment fee on unused amount 0.25%  
Interest calculation under revolving credit facility The rate is calculated based on LIBOR plus 1.75%  
Maximum [Member]
    
Line of Credit Facility [Line Items]    
Reduction in borrowing capacity 2,500,000  
Maximum [Member] | September 30, 2013 [Member]
    
Line of Credit Facility [Line Items]    
Funded debt to EBITDA ratio 2.25  
Maximum [Member] | Revolving Credit Facility [Member]
    
Line of Credit Facility [Line Items]    
Revolving credit facility current borrowing capacity $ 21,500,000  
Minimum [Member]
    
Line of Credit Facility [Line Items]    
Minimum Fixed Charge Coverage Ratio 1.25