Fair Values - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Assets
Derivatives	$ 1,628	$ 1,628	$ 4,086
Liabilities
Derivatives	7,167	$ 7,167	210
Recurring [Member]
Assets
Derivatives	1,628		4,086
Liabilities
Derivatives	7,167		210
Level 2 [Member] | Recurring [Member]
Assets
Derivatives	1,628		4,086
Liabilities
Derivatives	$ 7,167		$ 210