Derivative Financial Instruments - Effects of Derivative Instruments on Financial Statements (Detail) - Derivatives Designated as Hedges [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments Gain Loss [Line Items]
Amount of gain (loss) recognized in other comprehensive income (loss)	$ 4,610	$ (10,304)	$ 10,212	$ 10,230
Cost of operations [Member]
Derivative Instruments Gain Loss [Line Items]
(Loss) gain reclassified from AOCI	784	14,932	(2,731)	24,611
Other non-operating expense [Member]
Derivative Instruments Gain Loss [Line Items]
Ineffective portion and amount excluded from effectiveness testing: loss recognized	$ (1,225)	$ (344)	$ (919)	$ (1,549)