Derivative Financial Instruments (Details)	Sep. 30, 2013 bbl
Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	19,800,000
Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	224,400,000
Natural Gas Liquids
Derivative Financial Instruments
Portion of future oil and NGL production hedged	900,000
NYMEX WTI [Member]
Derivative Financial Instruments
Index percent of oil fixed swap	93.00%
Argus LLS [Member]
Derivative Financial Instruments
Index percent of oil fixed swap	7.00%
IF El Paso Permian [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	3.00%
Index percent of natural gas collars	2.00%
IF HSC [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	72.00%
Index percent of natural gas collars	54.00%
IF NGPL TXOK [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	3.00%
Index percent of natural gas collars	4.00%
IF NNG Ventura [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	2.00%
Index percent of natural gas collars	5.00%
IF PEPL [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	8.00%
Index percent of natural gas collars	7.00%
IF Reliant N/S [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	10.00%
Index percent of natural gas collars	15.00%
IF NGPL MidCont [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps	2.00%
IF TETCO STX [Member]
Derivative Financial Instruments
Index percent of natural gas collars	13.00%
OPIS Mont. Belvieu Ethane Purity [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	7.00%
OPIS Mont. Belvieu LDH Propane [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	45.00%
OPIS Mont. Belvieu Non LDH Isobutane [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	13.00%
OPIS Mont. Belvieu Non-LDH Normal Butane [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	16.00%
OPIS Mont. Belvieu Non-LDH Natural Gasoline [Member]
Derivative Financial Instruments
Index percent of NGL fixed swaps	19.00%
Swap | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	11,897,000
Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	202,584,000
Swap | Natural Gas Liquids
Derivative Financial Instruments
Portion of future oil and NGL production hedged	915,000
Collar | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	7,868,000
Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	21,854,000
Remainder of 2013 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	1,118,000
Weighted-Average Contract Price	97.09
Remainder of 2013 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	19,047,000
Weighted-Average Contract Price	4.06
Remainder of 2013 [Member] | Swap | Natural Gas Liquids
Derivative Financial Instruments
Portion of future oil and NGL production hedged	511,000
Weighted-Average Contract Price	53.16
Remainder of 2013 [Member] | Collar | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	1,480,000
Weighted-Average Floor Price	88.14
Weighted-Average Ceiling Price	114.12
Remainder of 2013 [Member] | Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	1,640,000
Weighted-Average Floor Price	4.39
Weighted-Average Ceiling Price	5.31
2014 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	5,164,000
Weighted-Average Contract Price	95.25
2014 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	64,453,000
Weighted-Average Contract Price	4.06
2014 [Member] | Swap | Natural Gas Liquids
Derivative Financial Instruments
Portion of future oil and NGL production hedged	404,000
Weighted-Average Contract Price	58.42
2014 [Member] | Collar | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	3,022,000
Weighted-Average Floor Price	84.07
Weighted-Average Ceiling Price	105.46
2014 [Member] | Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	5,734,000
Weighted-Average Floor Price	4.38
Weighted-Average Ceiling Price	5.36
2015 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	2,911,000
Weighted-Average Contract Price	89.06
2015 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	49,328,000
Weighted-Average Contract Price	4.04
2015 [Member] | Collar | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	3,366,000
Weighted-Average Floor Price	85.00
Weighted-Average Ceiling Price	94.25
2015 [Member] | Collar | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	14,480,000
Weighted-Average Floor Price	3.96
Weighted-Average Ceiling Price	4.30
2016 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of future oil and NGL production hedged	2,704,000
Weighted-Average Contract Price	85.19
2016 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	36,126,000
Weighted-Average Contract Price	4.18
2017 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	23,430,000
Weighted-Average Contract Price	4.21
2018 [Member] | Swap | Natural Gas
Derivative Financial Instruments
Portion of Gas Production Being Hedged	10,200,000
Weighted-Average Contract Price	4.31