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
	Mar. 31, 2018	Mar. 31, 2017
Derivatives, Fair Value [Line Items]
Gains recognized in OCI	$ 356	$ 2,887
Losses recognized in OCI	(510)	0
Gains recognized from accumulated OCI into net income	257	206
Losses recognized from accumulated OCI into net income	$ 0	$ (5)