Revolving Credit Facility and Long-Term Debt - Additional Information (Detail) - Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Jul. 01, 2018	Jun. 15, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Credit facility borrowing used	$ 5,900,000	$ 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					$ 0
Ratio of restricted and unrestricted cash and marketable securities to workers' compensation and safety incentive liabilities		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		$ 0.25
Dividend to be payable date				Jun. 30, 2019
Minimum [Member]
Line of Credit Facility [Line Items]
EBITDA	$ 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	$ 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	25,000,000	25,000,000		$ 25,000,000				$ 40,000,000
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%
Revolving Credit Facility [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity							$ 28,000,000
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity	6,000,000	6,000,000		$ 6,000,000
Standby Letters of Credit [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Credit facility borrowing capacity							$ 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		$ 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%		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		$ 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	$ 4,300,000	$ 4,300,000		$ 4,300,000					$ 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%