Revolving Credit Facility - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Line of credit facility expiration date	Oct. 01, 2017
Revolving credit facility borrowing capacity	$ 16,500,000
Letters of credit outstanding amount	27,600,000
Line of credit facility commitment fee description	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
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
Maximum [Member]
Line of Credit Facility [Line Items]
Reduction in borrowing capacity	2,500,000
Minimum [Member]
Line of Credit Facility [Line Items]
Minimum Fixed Charge Coverage Ratio	1.25
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings on the revolving credit facility	$ 0	$ 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%