Derivative Instruments - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount	$ 90,349,000	$ 41,197,000
Minimum [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative foreign currency exchange contracts durations	1 month
Maximum [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative foreign currency exchange contracts durations	3 months