Line of Credit - Additional Information (Detail) - Line of Credit	9 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Total availability under line of credit agreement	$ 10,000,000.0
Line of credit borrowings	0	$ 0
Letters of credit outstanding amount	2,700,000
Available borrowing under letter of credit	$ 7,300,000
Varying interest on line of credit agreement	LIBOR plus 1.75% or Prime less 0.50%
Maturity date of line of credit	Jul. 31, 2017
Maximum ratio of total liabilities to tangible net worth	1
Minimum required fixed coverage charge ratio	1.25
Trailing period used for calculating ratios	12 months
Company's leverage ratio	1.24
Fixed coverage charge ratio	3.88
London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread plus (minus) on variable interest rate	1.75%
Prime Rate
Debt Instrument [Line Items]
Basis spread plus (minus) on variable interest rate	(0.50%)