Derivative Instruments - Gains (Losses) on Derivative Instruments and Classification on Condensed Consolidated Statement of Operations (Detail) - Designated As Hedging Instrument [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivatives, Fair Value [Line Items]
Gains recognized in OCI	$ 0	$ 1,445	$ 356	$ 4,332
Losses recognized in OCI	(2,202)	(17)	(2,714)	(17)
Gains recognized from accumulated OCI into net income	60	782	317	988
Losses recognized from accumulated OCI into net income	$ (395)	$ (5)	$ (395)	$ (10)