Long-term Debt - Components of Borrowings, Including Current Portion (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Term loans payable	$ 50,446,000	$ 49,315,000
Unamortized debt issuance costs	(313,000)	(384,000)
Long-term debt, net of debt issuance costs	50,133,000	48,931,000
Term Loan Agreement
Debt Instrument [Line Items]
Term loans payable	50,400,000		$ 49,300,000
Long-term debt, net of debt issuance costs	$ 50,133,000	$ 48,931,000