Derivative Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2012

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of fair value of derivatives in accompanying balance sheets

The following tables detail the fair value of derivatives recorded in the accompanying balance sheets, by category:

	As of December 31, 2012
	Derivative Assets			Derivative Liabilities
	Balance Sheet  Classification	Fair Value		Balance Sheet  Classification	Fair Value
	(in thousands)
Commodity Contracts	Current assets	$	37,873	Current liabilities	$	8,999
Commodity Contracts	Noncurrent assets	16,466		Noncurrent liabilities	6,645
Derivatives not designated as hedging instruments		$	54,339		$	15,644

	As of December 31, 2011
	Derivative Assets			Derivative Liabilities
	Balance Sheet  Classification	Fair Value		Balance Sheet  Classification	Fair Value
	(in thousands)
Commodity Contracts	Current assets	$	55,813	Current liabilities	$	42,806
Commodity Contracts	Noncurrent assets	31,062		Noncurrent liabilities	12,875
Derivatives not designated as hedging instruments		$	86,875		$	55,681

Schedule of unrealized and realized gains and losses on derivative instruments in the statement of operations

The following table summarizes the components of unrealized and realized derivative (gain) loss presented in the accompanying statements of operations:

	For the Years Ended December 31,
	2012			2011
	(in thousands)
Cash settlement (gain) loss:
Oil contracts	$	11,893		$	22,633
Gas contracts	(47,270		)	(10,711		)
NGL contracts	(8,887		)	13,749
Total cash settlement (gain) loss	(44,264		)	25,671
Unrealized (gain) loss on change in fair value:
Oil contracts	(31,981		)	(3,391		)
Gas contracts	31,777			(64,310		)
NGL contracts	(11,162		)	4,944
Total net unrealized (gain) on change in fair value	(11,366		)	(62,757		)
Total unrealized and realized derivative (gain)	$	(55,630	)	$	(37,086	)

Detail of the effect of derivative instruments reclassified from AOCI to the statement of operations (net of income tax)

The following table details the effect of derivative instruments on AOCIL and the accompanying statements of operations (net of income tax):

		Location on Accompanying Statements of Operations	For the Years Ended December 31,
	Derivatives		2012			2011		2010
			(in thousands)
Amount reclassified from AOCIL	Commodity Contracts	Realized hedge gain (loss)	$	(2,264	)	$	12,997	$	6,641

Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location [Table Text Block]

The following table details the ineffective portion of derivative instruments classified as cash flow hedges on the accompanying statements of operations for the year ended December 31, 2010.

		Loss Recognized in Earnings (Ineffective Portion)
	Location on Accompanying  Statements of Operations
Derivatives Qualifying as Cash Flow Hedges
		For the Year Ended December 31, 2010
		(in thousands)
Commodity Contracts	Unrealized and realized derivative (gain) loss	$	8,899