Derivative Financial Instruments (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative Financial Instruments
Fair value of oil, natural gas, NGL commodity derivative markets	$ 80,600,000	$ 38,700,000	$ 80,600,000	$ 38,700,000
Derivative (gains) losses relating to de-designated commodity hedges reclassified from AOCL to earnings net of tax	746,000	(116,000)	807,000	(1,150,000)
Derivatives not designated as hedging instruments
Derivative Financial Instruments
Gains expected to be reclassifiied into earnings from AOCL after-tax net loss related to de-designated commodity derivative contracts			$ 300,000
Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	12,600,000		12,600,000
Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	167,200,000		167,200,000
Natural Gas Liquids
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	1,500,000		1,500,000
NYMEX WTI [Member]
Derivative Financial Instruments
Index percent of oil fixed swap	71.00%		71.00%
Argus LLS [Member]
Derivative Financial Instruments
Index percent of oil fixed swap	29.00%		29.00%
IF El Paso Permian [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	3.00%		3.00%
Index percent of natural gas collars	2.00%		2.00%
IF HSC [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	58.00%		58.00%
Index percent of natural gas collars	51.00%		51.00%
IF NGPL TXOK [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	5.00%		5.00%
Index percent of natural gas collars	6.00%		6.00%
IF NNG Ventura [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	3.00%		3.00%
Index percent of natural gas collars	4.00%		4.00%
IF PEPL [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	13.00%		13.00%
Index percent of natural gas collars	6.00%		6.00%
IF Reliant N/S [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	15.00%		15.00%
Index percent of natural gas collars	17.00%		17.00%
IF TETCO STX [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	1.00%		1.00%
Index percent of natural gas collars	14.00%		14.00%
IF NGPL MidCont [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	2.00%		2.00%
OPIS Mont. Belvieu Ethane Purity [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	9.00%		9.00%
OPIS Mont. Belvieu LDH Propane [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	44.00%		44.00%
OPIS Mont. Belvieu Non LDH Isobutane [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	12.00%		12.00%
OPIS Mont. Belvieu Non-LDH Normal Butane [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	16.00%		16.00%
OPIS Mont. Belvieu Non-LDH Natural Gasoline [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	19.00%		19.00%
Swap | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	4,763,000		4,763,000
Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	143,578,000		143,578,000
Swap | Natural Gas Liquids
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	1,481,000		1,481,000
Collar | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	7,879,000		7,879,000
Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	23,624,000		23,624,000
Remainder of 2013 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	2,383,000		2,383,000
Weighted-Average Contract Price	97.51		97.51
Remainder of 2013 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	40,335,000		40,335,000
Weighted-Average Contract Price	4.00		4.00
Remainder of 2013 [Member] | Swap | Natural Gas Liquids
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	1,077,000		1,077,000
Weighted-Average Contract Price	53.26		53.26
Remainder of 2013 [Member] | Collar | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	1,491,000		1,491,000
Weighted-Average Floor Price	77.88		77.88
Weighted-Average Ceiling Price	111.93		111.93
Remainder of 2013 [Member] | Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	3,410,000		3,410,000
Weighted-Average Floor Price	4.39		4.39
Weighted-Average Ceiling Price	5.31		5.31
2014 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	2,024,000		2,024,000
Weighted-Average Contract Price	93.85		93.85
2014 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	59,384,000		59,384,000
Weighted-Average Contract Price	4.08		4.08
2014 [Member] | Swap | Natural Gas Liquids
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	404,000		404,000
Weighted-Average Contract Price	58.42		58.42
2014 [Member] | Collar | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	3,022,000		3,022,000
Weighted-Average Floor Price	84.07		84.07
Weighted-Average Ceiling Price	105.46		105.46
2014 [Member] | Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	5,734,000		5,734,000
Weighted-Average Floor Price	4.38		4.38
Weighted-Average Ceiling Price	5.36		5.36
2015 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	356,000		356,000
Weighted-Average Contract Price	88.40		88.40
2015 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	33,528,000		33,528,000
Weighted-Average Contract Price	4.07		4.07
2015 [Member] | Collar | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	3,366,000		3,366,000
Weighted-Average Floor Price	85.00		85.00
Weighted-Average Ceiling Price	94.25		94.25
2015 [Member] | Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	14,480,000		14,480,000
Weighted-Average Floor Price	3.96		3.96
Weighted-Average Ceiling Price	4.30		4.30
2016 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	10,331,000		10,331,000
Weighted-Average Contract Price	4.38		4.38