Derivative Financial Instruments - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Net gain (loss) on derivative financial instruments	$ (5,159,000)	$ (25,082,000)
Net deferred losses expected to be reclassified from AOCI over next 12 months	(2,000,000)
Notional value of outstanding derivative contracts	$ 215,000,000
Derivative contracts, maturity date	Mar. 31, 2019
Fair value of derivative contracts	$ 3,000,000
EPCI projects [Member]
Derivative [Line Items]
Notional value of outstanding derivative contracts	$ 89,000,000