Credit Agreement - Additional Information (Detail) - Credit Agreement [Member] - USD ($)			1 Months Ended	3 Months Ended
	Sep. 29, 2016	Sep. 22, 2015	Sep. 30, 2016	Mar. 31, 2018	Dec. 31, 2017
Line Of Credit Facility [Line Items]
Letter of credit, agreement amount			$ 250,000
Unsecured Line of Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Line of credit, interest rate description				The Credit Agreement shall bear interest at either (1) a rate per annum equal to 1.5% below the bank’s applicable prime rate or (2) 1.5% above the Bank’s applicable LIBOR rate, in each case as defined in the Credit Agreement.
Line of credit, final due date	Sep. 22, 2018
Line of credit, amount outstanding				$ 0	$ 0
Unsecured Line of Credit Agreement [Member] | Prime Rate [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Line of credit, interest rate, basis spread on variable rate				1.50%
Unsecured Line of Credit Agreement [Member] | LIBOR Rate [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Line of credit, interest rate, basis spread on variable rate				1.50%
Unsecured Line of Credit Agreement [Member] | JPMorgan Chase Bank, N.A. [Member]
Line Of Credit Facility [Line Items]
Line of credit, term		2 years
Line of credit, maximum borrowing capacity		$ 12,000,000	$ 11,750,000