Financial Instruments and Risk Management - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Term of currency derivative	Less than one year

Description of the relevant terms of the derivative. Includes the type of instrument, risk being hedged, notional amount, counterparty, inception date, maturity date, relevant interest rates, strike price, cap price, and floor price.

No definition available.

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