Indebtedness (Narrative) (Details) (USD $)	12 Months Ended			12 Months Ended							12 Months Ended						0 Months Ended							12 Months Ended
	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Revolving Credit Facility [Member]	Jan. 17, 2014 Revolving Credit Facility [Member]	Nov. 26, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Oct. 31, 2012 Revolving Credit Facility [Member]	May 01, 2012 Revolving Credit Facility [Member]	Feb. 14, 2011 Revolving Credit Facility [Member]	Dec. 31, 2013 Minimum [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Maximum [Member] Revolving Credit Facility [Member]	Dec. 31, 2011 Parent Company [Member]	Dec. 31, 2013 8.25% Senior Notes [Member]	Dec. 31, 2013 8.25% Senior Notes [Member] Minimum [Member]	Dec. 31, 2013 8.25% Senior Notes [Member] Maximum [Member]	Feb. 14, 2011 ASOP Acquisition [Member]	Feb. 14, 2011 ASOP Acquisition [Member] 2011 Senior Notes [Member]	Oct. 31, 2012 Hilcorp Acquisition [Member]	Oct. 31, 2012 Hilcorp Acquisition [Member]	Oct. 31, 2012 Hilcorp Acquisition [Member] Senior Notes Due 2018 [Member]	Oct. 25, 2011 Hilcorp Acquisition [Member] Senior Notes Due 2018 [Member]	Oct. 25, 2012 Hilcorp Acquisition [Member] Senior Notes Due 2018 [Member]	Dec. 31, 2013 Base Rate plus margin [Member] Minimum [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Base Rate plus margin [Member] Maximum [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 LIBOR plus margin [Member] Minimum [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 LIBOR plus margin [Member] Maximum [Member] Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Senior Notes, face amount														$ 510,000,000				$ 210,000,000			$ 300,000,000		$ 300.0
Senior Notes, stated percentage														8.25%
Maturity date				Oct. 31, 2016										Feb. 15, 2018
Net proceeds from offering of Notes																		202,000,000			289,500,000	289,500,000
Loss on early extinguishment of debt	2,377,000												2,377,000
Purchase price of properties																	200,700,000	200,700,000	550,000,000	550,000,000
Acquired certain interests in producing oil and natural gas assets																	200,700,000	200,700,000	550,000,000	550,000,000
Line of Credit Facility, Maximum Borrowing Capacity				750,000,000				750,000,000		250,000,000
Borrowing base under the expanded credit facility					475,000,000	425,000,000		425,000,000	200,000,000
Line Of Credit Facility Increase To Current Borrowing Capacity					50,000,000
Debt Instrument, Basis Spread on Variable Rate																								0.75%	1.75%	1.75%	2.75%
Amounts drawn under Senior Credit Facility				130,000,000			195,000,000
Senior credit facility condition				Our obligations under our Senior Credit Facility, as well as any hedging contracts and treasury management agreements with the lenders or affiliates of lenders, are secured by substantially all of our assets, including a) mortgages on at least 80% of the total value of our oil and gas properties evaluated in the most recently completed reserve report, after giving effect to exploration and production activities, acquisitions and dispositions, and b) the stock of certain wholly-owned subsidiaries.
Debt redemption notice															30 days	60 days
Redeemable debt, redemption percentage of principal prior to 2014																35.00%
Early debt redemption notice															30 days	60 days
Redeemable debt, redemption percentage prior to 2014														108.25%
Redeemable debt, percentage of principal outstanding prior to 2014															65.00%
Redeemable debt, redemption period after equity offering														90 days
Minimum debt owned for repurchase right														2,000
Minimum debt owned for repurchase right, additional increments														1,000
Repurchase right, redemption percentage														101.00%
Repurchase period after sale of assets														360 days
Minimum proceeds from sale of assets that must be applied to senior notes														20,000,000
Repurchase Percentage of Senior Notes														100.00%
Commitment fees											0.375%	0.50%
Line of Credit Facility Maximum Letter of Credit Capacity				20,000,000
Covenant certification requirements				Our Senior Credit Facility contains customary covenants, default provisions and collateral requirements. As described in the agreement underlying our Senior Credit Facility, we must maintain, for each period for which a covenant certification is required, (a) a minimum current ratio (as defined in the agreement for our Senior Credit Facility) of 1.0 to 1.0 and (b) a maximum total debt to EBITDAX ratio of 3.5 to 1.0. We are also required to maintain a commodities hedging program that is in compliance with the requirements set forth in our Senior Credit Facility. Our Senior Credit Facility also places restrictions on the maximum estimated future production volumes that can be subject to commodity derivative instruments.
Effective interest rate														9.10%
Accrued interest included in purchase price		$ 15,800,000	$ 16,200,000																				$ 4,800,000