Derivative Financial Instruments - Schedule of Notional Amounts of Derivatives (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional amounts	$ 10,743,000	$ 21,672,000

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant