Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Value [Member] | Other Current Assets [Member]
Assets:
Derivative assets		$ 5,179
Carrying Value [Member] | Other Current Liabilities [Member]
Liabilities:
Derivative liabilities	$ 2,595
Estimate of Fair Value Measurement [Member] | Other Current Assets [Member]
Assets:
Derivative assets		5,179
Estimate of Fair Value Measurement [Member] | Other Current Liabilities [Member]
Liabilities:
Derivative liabilities	2,595
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Assets [Member]
Assets:
Derivative assets		$ 5,179
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Liabilities [Member]
Liabilities:
Derivative liabilities	$ 2,595