Derivative Instruments - Reconciles Net Amounts Derivative Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative assets	$ 12,587	$ 93,922
Noncurrent derivative assets	1,676	14,560
Net amounts of assets on balance sheet	14,263	108,482
Derivative liabilities	(13,780)	(3,583)
Noncurrent derivative liabilities	(4,299)	(3,706)
Net amounts of liabilities on balance sheet	(18,079)	(7,289)
Total derivative assets, net	$ (3,816)	$ 101,193