Fair Value Measurements of Financial Assets and Liabilities on Recurring and Non Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liabilities:
Derivative instruments	$ (2,537)	$ (3,468)
Total fair value	(2,537)	(3,468)
Fair Value, Inputs, Level 2
Liabilities:
Derivative instruments	(2,537)	(3,468)
Total fair value	$ (2,537)	$ (3,468)