Long-term Debt - Components of Borrowings, Including Current Portion (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Term loans payable	$ 49,685	$ 49,315
Unamortized debt issuance costs	(360)	(384)
Long-term debt, net of debt issuance costs	49,325	48,931
Term Loan Agreement
Debt Instrument [Line Items]
Term loans payable	49,700		$ 49,300
Long-term debt, net of debt issuance costs	$ 49,325	$ 48,931