Fair Value Measurements - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Derivative maturities	4 years
Effective portion of change in fair value of foreign currency forward contracts	$ 180,000	$ (2,640,000)
Long-term debt, fair market value	318,418,000	329,329,000
Long-term debt, carrying value	$ 295,017,000	295,987,000
Foreign Exchange Contracts
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Derivative maturities	4 years
Notional amount of the foreign currency derivative instruments	$ 174,924,000	$ 134,530,000
Foreign Exchange Contracts | Maximum
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Maturities of forward contracts	12 months