Derivative Financial Instruments - Effects of Derivative Instruments on Financial Statements (Detail) - Derivatives Designated as Hedges [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments Gain Loss [Line Items]
Amount of gain (loss) recognized in other comprehensive income (loss)	$ 4,971	$ 4,228	$ 15,183	$ 14,458
Cost of operations [Member]
Derivative Instruments Gain Loss [Line Items]
Loss (gain) reclassified from AOCI to Cost of operations	4,209	(679)	1,478	23,932
Other non-operating expense [Member]
Derivative Instruments Gain Loss [Line Items]
Ineffective portion and amount excluded from effectiveness testing: gain (loss) recognized	$ (226)	$ 1,830	$ (1,145)	$ 281