Derivatives - Open Commodity Derivative Contracts (Detail)	Mar. 31, 2013 MBbls
Oil \| Price Swap \| April 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	10,142
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	98.64
Oil \| Price Swap \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	7,511
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	92.43
Oil \| Price Swap \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	5,076
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	83.69
Oil \| Basis Swaps \| April 2013 - June 2013
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	273
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	12.51
Oil \| Two-Way Collars \| April 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	126
Collar Range, minimum	80.00
Collar Range, maximum	102.50
Oil \| Three-Way Collars \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	8,213
Oil \| Three-Way Collars \| January 2014 - December 2014 \| Sold put
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Collar Range, minimum	70.00
Oil \| Three-Way Collars \| January 2014 - December 2014 \| Purchased put
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Collar Range, minimum	90.20
Oil \| Three-Way Collars \| January 2014 - December 2014 \| Sold call
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Collar Range, maximum	100.00
Oil \| Three-Way Collars \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	2,920
Oil \| Three-Way Collars \| January 2015 - December 2015 \| Sold put
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Collar Range, minimum	73.13
Oil \| Three-Way Collars \| January 2015 - December 2015 \| Purchased put
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Collar Range, minimum	90.82
Oil \| Three-Way Collars \| January 2015 - December 2015 \| Sold call
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Collar Range, maximum	103.13
Natural Gas \| Price Swap \| April 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	31,005
Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)	4.01
Natural Gas \| Collars \| April 2013 - December 2013
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	5,146
Collar Range, minimum	3.78
Collar Range, maximum	6.71
Natural Gas \| Collars \| January 2014 - December 2014
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	937
Collar Range, minimum	4.00
Collar Range, maximum	7.78
Natural Gas \| Collars \| January 2015 - December 2015
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional (Oil in MBbls/Natural Gas in MMcf)	1,010
Collar Range, minimum	4.00
Collar Range, maximum	8.55

Derivatives - Open Commodity Derivative Contracts (Detail)

Mar. 31, 2013

MBbls

Oil | Price Swap | April 2013 - December 2013

Derivative Instruments and Hedging Activities Disclosure [Line Items]

Notional (Oil in MBbls/Natural Gas in MMcf)

10,142

Weighted Avg. Fixed Price (Oil in USD/bbl, Natural Gas in USD/mcf)

98.64

Oil | Price Swap | January 2014 - December 2014

Derivative Instruments and Hedging Activities Disclosure [Line Items]

Notional (Oil in MBbls/Natural Gas in MMcf)