Revolving Credit Facility and Long-Term Debt - Additional Information (Detail) - Agreement [Member] - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Line of credit facility commitment fee description					The Agreement also provides for an unused commitment fee of 0.35% per year through December 31, 2016 and 0.375% per year thereafter on the average daily unused amount of the revolving credit facility, and a fee of 1.75% of the face amount of each letter of credit reserved under the line of credit and 0.95% on standalone, fully secured letters of credit.
Restricted certificates of deposit, current					$ 5,300,000
Maximum amount of capital expenditures in 2016					4,000,000
Maximum [Member]
Line of Credit Facility [Line Items]
Prohibition on incurring additional indebtedness without the prior approval of the Bank in purchase money financing					$ 1,000,000
Scenario Forecast [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
EBITDA	$ 25,000,000	$ 25,000,000	$ 25,000,000	$ 22,000,000
Ratio of restricted and unrestricted cash and marketable securities to workers’ compensation and safety incentive liabilities	100.00%	100.00%	100.00%	100.00%
Term Loan [Member]
Line of Credit Facility [Line Items]
Outstanding balance on term loan and revolving credit facility						$ 15,000,000
Term loan from Bank, Interest rate description					One month LIBOR plus 2.25%
Term loan with principal bank					$ 4,600,000	4,800,000
Payment of monthly principal of term loan					$ 18,375
Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
LIBOR plus rate					2.25%
Term Loan [Member] | Wells Fargo [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity					$ 40,000,000
Term loan maturity date					Dec. 31, 2016
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Outstanding balance on term loan and revolving credit facility					$ 0	$ 0
Unused commitment fee on unused amount during period					0.35%
Unused commitment fee on unused amount after amendment					0.375%
Credit facility, expiration date					Jul. 01, 2018
Revolving Credit Facility [Member] | Daily Floating Rate [Member]
Line of Credit Facility [Line Items]
Term loan from Bank, Interest rate description					A daily floating rate of one month LIBOR plus 1.75%
LIBOR plus rate					1.75%
Revolving Credit Facility [Member] | Fixed Rate [Member]
Line of Credit Facility [Line Items]
Term loan from Bank, Interest rate description					A fixed rate of LIBOR plus 1.75%
LIBOR plus rate					1.75%
Revolving Credit Facility [Member] | Wells Fargo [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity					$ 25,000,000
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing used					5,300,000
Standby Letters of Credit [Member] | Wells Fargo [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity					$ 6,000,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Unused commitment fee on unused amount					1.75%
Fully Secured Letter of Credit [Member]
Line of Credit Facility [Line Items]
Unused commitment fee on unused amount					0.95%
Fully Secured Letter of Credit [Member] | Wells Fargo [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity					$ 5,000,000