Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying Value [Member] | Other Current Liabilities [Member]
Liabilities:
Derivative liabilities		$ 453
Carrying Value [Member] | Other Current Assets [Member]
Assets:
Derivative assets	$ 5,179
Estimate of Fair Value Measurement [Member] | Other Current Liabilities [Member]
Liabilities:
Derivative liabilities		453
Estimate of Fair Value Measurement [Member] | Other Current Assets [Member]
Assets:
Derivative assets	5,179
Significant Other Observable Inputs (Level 2) [Member] | Other Current Liabilities [Member]
Liabilities:
Derivative liabilities		$ 453
Significant Other Observable Inputs (Level 2) [Member] | Other Current Assets [Member]
Assets:
Derivative assets	$ 5,179