Derivative Instruments - Realized and Unrealized Gains and Losses from Commodity Derivative Instruments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Total net gain (loss) on derivative instruments	$ 210,376	$ 327,011	$ (35,432)