Derivative Financial Instruments - Offsetting of Derivative Liabilities (Detail) - Zero Cost Collars [Member] $ in Thousands	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Liability Derivatives, Gross amounts of recognized liabilities	$ 453
Liability Derivatives, Gross amounts offset in the balance sheets	0
Liability Derivatives, Net amounts of liabilities presented in the balance sheets	453
Liability Derivatives, Gross amounts not offset in the balance sheets, Financial instruments	0
Liability Derivatives, Gross amounts not offset in the balance sheets, Cash collateral pledged	(650)
Liability Derivatives, Net amount after master netting	$ (197)