Derivative Financial Instruments - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net gain (loss) on derivative financial instruments	$ 33,229,000	$ 58,316,000	$ (11,735,000)
Net deferred gains expected to be reclassified from AOCI over next 12 months	10,200,000
Notional value of outstanding derivative contracts	1,300,000,000
Derivative contracts, maturity date	Dec. 31, 2017
Fair value of Derivative contracts	17,600,000
EPCI projects
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional value of outstanding derivative contracts	$ 721,600,000