Fair Value Measurements - Derivative Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, at beginning of period	$ (25,867)	$ (21,254)	$ (29,316)
Settlements	16,810	7,691	780
Acquired	0	(2,844)	0
Total unrealized income (loss) included in earnings	(16,077)	(9,460)	7,282
Balance, at end of period	$ (25,134)	$ (25,867)	$ (21,254)