Long-Term Debt (Details) (USD $)	3 Months Ended	12 Months Ended										12 Months Ended					12 Months Ended				12 Months Ended	1 Months Ended				1 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Revolving credit facility, due November 2015 Quarter	Nov. 30, 2012 Revolving credit facility, due November 2015	Aug. 31, 2012 Revolving credit facility, due November 2015	May 31, 2012 Revolving credit facility, due November 2015	Apr. 30, 2012 Revolving credit facility, due November 2015	Mar. 31, 2012 Revolving credit facility, due November 2015	Dec. 31, 2011 Revolving credit facility, due November 2015	Dec. 31, 2012 Revolving credit facility, due November 2015 Minimum	Dec. 31, 2012 Revolving credit facility, due November 2015 Maximum installment	Dec. 31, 2012 Revolving credit facility, due November 2015 LIBOR	Dec. 31, 2012 Revolving credit facility, due November 2015 LIBOR Minimum	Dec. 31, 2012 Revolving credit facility, due November 2015 LIBOR Maximum	Dec. 31, 2012 Revolving credit facility, due November 2015 Prime rate	Dec. 31, 2012 Revolving credit facility, due November 2015 Federal funds rate	Dec. 31, 2012 Revolving credit facility, due November 2015 Base rate Minimum	Dec. 31, 2012 Revolving credit facility, due November 2015 Base rate Maximum	Dec. 31, 2012 Revolving credit facility, due November 2015 One-month LIBOR	Aug. 31, 2011 7 3/4% Senior Notes due 2013	Mar. 31, 2011 7 3/4% Senior Notes due 2013	Jul. 31, 2005 7 3/4% Senior Notes due 2013	Dec. 31, 2012 7 3/4% Senior Notes due 2013	Apr. 30, 2011 7.75% Senior Notes due 2019	Mar. 31, 2011 7.75% Senior Notes due 2019	Dec. 31, 2012 7.75% Senior Notes due 2019	Dec. 31, 2011 7.75% Senior Notes due 2019	Dec. 31, 2012 7.75% Senior Notes due 2019 Beginning on April 1, 2015	Dec. 31, 2012 7.75% Senior Notes due 2019 Beginning on April 1, 2016	Dec. 31, 2012 7.75% Senior Notes due 2019 On or after April 1, 2017
Long-Term Debt
Long-term debt	$ 809,585,000	$ 809,585,000	$ 529,535,000		$ 460,000,000						$ 180,000,000																	$ 349,585,000	$ 349,535,000
Aggregate maturities of long term debt in 2015	460,000,000	460,000,000
Aggregate maturities of long term debt in 2019	349,600,000	349,600,000
Unamortized original issue discount																										500,000		415,000	465,000
Maximum borrowing capacity					585,000,000	585,000,000		565,000,000	500,000,000
Number of equal monthly installments to prepay the deficiency													5
Borrowing base						585,000,000		565,000,000	475,000,000
Aggregate commitment amount						585,000,000	555,000,000		475,000,000	350,000,000
Outstanding letters of credit					4,100,000
Amount available under the revolving credit facility					121,000,000
Increased indebtedness outstanding					280,000,000
Percentage of adjusted engineered value of oil and gas interests serving as collateral												80.00%
Variable rate basis														LIBOR			prime rate	federal funds rate			one-month LIBOR
Applicable margin (as a percent)															1.75%	2.75%		0.50%	0.75%	1.75%	1.00%
Commitment fee on unused portion (as a percent)												0.375%	0.50%
Effective annual interest rate (as a percent)					2.70%
Current ratio												1
Number of consecutive quarters for which ratio of consolidated funded indebtedness to consolidated EBITDAX is required to be maintained					4
Consolidated funded indebtedness to consolidated EBITDAX ratio													4
Aggregate principal amount of notes issued																								225,000,000		50,000,000	300,000,000
Interest rate (as a percent)																									7.75%	7.75%	7.75%
Principal redeemed																						81,800,000	143,200,000
Loss on early extinguishment of long-term debt	0	0	5,501,000	0																		907,000	4,600,000
Redemption premium paid for early extinguishment of long-term debt		0	2,765,000	0																			2,800,000
Write-off of debt issuance costs																							$ 1,800,000
Original issue discount (as a percent)																										1.00%
Redemption price of debt instrument (as a percent)																														103.875%	101.938%	100.00%