Derivative Financial Instruments (Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions) (Detail) bbl in Thousands, MMBTU in Thousands, $ in Thousands	Dec. 31, 2015 USD ($) MMBTU bbl	Dec. 31, 2014 USD ($) MMBTU bbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	1,184	470
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 12,650	$ 14,357
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	45	197
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (352)	$ (1,670)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	760	12,235
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 560	$ 12,707
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	0	16,755
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ 0	$ (4,095)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	45	197
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 354	$ 1,670
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	1,184	470
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (12,454)	$ (14,318)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	0	16,755
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 0	$ 4,095
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	760	12,235
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (549)	$ (12,646)