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, 2016 USD ($) MMBTU bbl	Dec. 31, 2015 USD ($) MMBTU bbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	227	1,184
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 206	$ 12,650
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	944	45
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (4,400)	$ (352)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	0	760
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 0	$ 560
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	1,299	0
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (1,357)	$ 0
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	944	45
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 4,580	$ 354
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	227	1,184
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (206)	$ (12,454)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	1,299	0
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 1,393	$ 0
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	0	760
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ 0	$ (549)