Revolving Credit Facility and Long-Term Debt - Additional Information (Detail) - Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended				9 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Jul. 01, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Credit facility borrowing used			$ 5,900,000			$ 5,900,000
Line of credit facility commitment fee description						The Agreement also provides for an unused commitment fee of 0.375% per year on the average daily unused amount of the revolving credit line, as well as 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.
Outstanding balance on term loan and revolving credit facility			$ 0			$ 0		$ 0
Ratio of restricted and unrestricted cash and marketable securities to workers' compensation and safety incentive liabilities			100.00%	100.00%	100.00%
Line of credit facility dividend restrictions						the Company may not declare or pay any dividend in excess of $0.25 per share in total each fiscal quarter, subject to increase by no more than 10% each year beginning June 30, 2019, compared to the prior fiscal year
Dividends, per share			$ 0.25			$ 0.25
Dividend to be payable date						Jun. 30, 2019
Scenario Forecast [Member]
Line of Credit Facility [Line Items]
Ratio of restricted and unrestricted cash and marketable securities to workers' compensation and safety incentive liabilities		100.00%
Minimum [Member]
Line of Credit Facility [Line Items]
EBITDA	$ 30,000,000		$ 30,000,000	$ 30,000,000	$ 30,000,000	$ 30,000,000
Minimum [Member] | Scenario Forecast [Member]
Line of Credit Facility [Line Items]
EBITDA		$ 30,000,000
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
Percentage of dividend payable						10.00%
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity							$ 28,000,000
Credit facility, expiration date						Jul. 01, 2020
Unused commitment fee on unused amount during period						0.375%
Revolving Credit Facility [Member] | Daily Floating Rate [Member]
Line of Credit Facility [Line Items]
Term loan from Bank, Interest rate description						the 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						the fixed rate of LIBOR plus 1.75%
LIBOR plus rate						1.75%
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity			$ 7,500,000			$ 7,500,000	$ 7,500,000
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%
Chubb Letter of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity	$ 63,700,000			$ 63,700,000
Credit facility, expiration date	Jul. 01, 2019
Percentage of initial fee under letter of credit						2.50%
Percentage of aggregate fee under letter of credit						95.00%
Percentage of annual fee under letter of credit			1.25%			1.25%
Chubb Letter of Credit [Member] | Collateral Accounts [Member]
Line of Credit Facility [Line Items]
Percentage of deposit in collateral accounts						50.00%
Chubb Letter of Credit [Member] | Collateral Accounts [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Deposit in collateral accounts			$ 16,000,000			$ 16,000,000
Term Loan [Member]
Line of Credit Facility [Line Items]
Term loan from Bank, Interest rate description						one month LIBOR plus 2.0%
Term loan with principal bank			$ 4,200,000			$ 4,200,000		$ 4,400,000
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						2.00%