Derivative Financial Instruments - Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions (Detail) bbl in Thousands, MMBTU in Thousands, $ in Thousands	Mar. 31, 2018 USD ($) MMBTU bbl	Dec. 31, 2017 USD ($) MMBTU bbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | bbl	462	253
Oil/Natural Gas Derivative Liabilities, Notional Amount | bbl	2,663	2,731
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 1,676	$ 193
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (19,122)	$ (13,448)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | MMBTU	6,963	5,927
Oil/Natural Gas Derivative Liabilities, Notional Amount | MMBTU	6,230	3,917
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 984	$ 1,399
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (591)	$ (326)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | bbl	2,699	2,731
Oil/Natural Gas Derivative Liabilities, Notional Amount | bbl	426	253
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 19,301	$ 13,709
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (1,668)	$ (187)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | MMBTU	6,133	3,917
Oil/Natural Gas Derivative Liabilities, Notional Amount | MMBTU	7,060	5,927
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 602	$ 340
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (975)	$ (1,366)