Commodity Derivative Positions (Detail) - Crude Oil $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) bbl $ / bbl
Derivative Instruments Related to Oil and Gas Production [Line Items]
Derivative, Swap Type, Average Fixed Price | $ / bbl	48.62
Third quarter 2016
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	5,940
Derivative, Swap Type, Average Fixed Price | $ / bbl	47.69
Fair Value Asset	$ 0
Fair Value Liability	$ 807
Fourth quarter 2016
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	5,940
Derivative, Swap Type, Average Fixed Price | $ / bbl	47.69
Fair Value Asset	$ 0
Fair Value Liability	$ 1,628
First Quarter 2017 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	4,408
Derivative, Swap Type, Average Fixed Price | $ / bbl	48.62
Fair Value Asset	$ 0
Fair Value Liability	$ 1,178
Second Quarter 2017 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	4,408
Derivative, Swap Type, Average Fixed Price | $ / bbl	48.62
Fair Value Asset	$ 0
Fair Value Liability	$ 1,390
Third Quarter 2017 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	4,408
Derivative, Swap Type, Average Fixed Price | $ / bbl	48.62
Fair Value Asset	$ 0
Fair Value Liability	$ 1,551
Fourth Quarter 2017 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	4,408
Derivative, Swap Type, Average Fixed Price | $ / bbl	48.62
Fair Value Asset	$ 0
Fair Value Liability	$ 1,721
First Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	3,476
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.12
Fair Value Asset	$ 0
Fair Value Liability	$ 1,252
Second Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	3,476
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.12
Fair Value Asset	$ 0
Fair Value Liability	$ 1,329
Third Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	3,476
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.12
Fair Value Asset	$ 0
Fair Value Liability	$ 1,410
Fourth Quarter 2018 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	3,476
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.12
Fair Value Asset	$ 0
Fair Value Liability	$ 1,485
First Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	2,916
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.90
Fair Value Asset	$ 0
Fair Value Liability	$ 1,056
Second Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	2,916
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.90
Fair Value Asset	$ 0
Fair Value Liability	$ 1,098
Fourth Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	2,916
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.90
Fair Value Asset	$ 0
Fair Value Liability	$ 1,195
Third Quarter 2019 [Member]
Derivative Instruments Related to Oil and Gas Production [Line Items]
Instrument	Swaps
Notional Volume, per day | bbl	2,916
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.90
Fair Value Asset	$ 0
Fair Value Liability	$ 1,142