| **Derivative Financial Instruments**                                        | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           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| **Derivative Instruments Not Designated as Hedging Instruments [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   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| Derivative Instruments and Hedging Activities Disclosure [Text Block]       | DERIVATIVE FINANCIAL INSTRUMENTSOur results of operations and operating cash flows are affected by changes in market prices for crude oil, natural gas and NGLs. To manage a portion of our exposure to price volatility from producing crude oil and natural gas, we utilize the following economic hedging strategies for each of our business segments.•For crude oil and natural gas sales, we enter into derivative contracts to protect against price declines in future periods. While we structure these derivatives to reduce our exposure to changes in price associated with the derivative commodity, they also limit the benefit we might otherwise have received from price increases in the physical market; and •For natural gas marketing, we enter into fixed-price physical purchase and sale agreements that qualify as derivative contracts. In order to offset the fixed-price physical derivatives in our natural gas marketing, we enter into financial derivative instruments that have the effect of locking in the prices we will receive or pay for the same volumes and period, offsetting the physical derivative. We believe our derivative instruments continue to be effective in achieving the risk management objectives for which they were intended. As of June 30, 2016, we had derivative instruments, which were comprised of collars, fixed-price swaps, basis protection swaps and physical sales and purchases, in place for a portion of our anticipated production through 2018 for a total of 71,560 BBtu of natural gas and 9,214 MBbls of crude oil. The majority of our derivative contracts are entered into at no cost to us as we hedge our anticipated production at the then-prevailing commodity market prices.We have not elected to designate any of our derivative instruments as hedges, and therefore do not qualify for use of hedge accounting. Accordingly, changes in the fair value of our derivative instruments are recorded in the statements of operations. Changes in the fair value of derivative instruments related to our Oil and Gas Exploration and Production segment are recorded in commodity price risk management, net. Changes in the fair value of derivative instruments related to our Gas Marketing segment are recorded in sales from and cost of natural gas marketing.The following table presents the balance sheet location and fair value amounts of our derivative instruments on the condensed consolidated balance sheets:     Fair ValueDerivative instruments: Balance sheet line item June 30, 2016 December 31, 2015     (in thousands)Derivative assets:Current       Commodity contracts       Related to crude oil and natural gas sales Fair value of derivatives $98,526 $221,161 Related to natural gas marketing Fair value of derivatives 313 441 Basis protection contracts       Related to crude oil and natural gas sales Fair value of derivatives — 57     98,839 221,659 Non-current       Commodity contracts       Related to crude oil and natural gas sales Fair value of derivatives 12,673 44,292 Related to natural gas marketing Fair value of derivatives 72 51 Basis protection contracts       Related to crude oil and natural gas sales Fair value of derivatives — 44     12,745 44,387Total derivative assets    $111,584 $266,046        Derivative liabilities:Current       Commodity contracts       Related to crude oil and natural gas sales Fair value of derivatives $21,179 $— Related to natural gas marketing Fair value of derivatives 251 417 Basis protection contracts       Related to crude oil and natural gas sales Fair value of derivatives 1,394 1,178     22,824 1,595 Non-current       Commodity contracts       Related to crude oil and natural gas sales Fair value of derivatives 26,509 275 Related to natural gas marketing Fair value of derivatives 54 46 Basis protection contracts       Related to crude oil and natural gas sales Fair value of derivatives 267 374     26,830 695Total derivative liabilities    $49,654 $2,290    The following table presents the impact of our derivative instruments on our condensed consolidated statements of operations:  Three Months Ended June 30, Six Months Ended June 30,Condensed consolidated statement of operations line item 2016 2015 2016 2015  (in thousands)Commodity price risk management gain (loss), net        Net settlements $53,301 $44,049 $120,132 $94,461Net change in fair value of unsettled derivatives (146,102) (93,090) (201,877) (76,840)Total commodity price risk management gain (loss), net $(92,801) $(49,041) $(81,745) $17,621Sales from natural gas marketing        Net settlements $53 $165 $298 $396Net change in fair value of unsettled derivatives (299) (124) (519) (293)Total sales from natural gas marketing $(246) $41 $(221) $103Cost of natural gas marketing        Net settlements $(49) $(157) $(277) $(375)Net change in fair value of unsettled derivatives 346 115 571 264Total cost of natural gas marketing $297 $(42) $294 $(111)         All of our financial derivative agreements contain master netting provisions that provide for the net settlement of all contracts through a single payment in the event of early termination. Our fixed-price physical purchase and sale agreements that qualify as derivative contracts are not subject to master netting provisions and are not significant. We have elected not to offset the fair value positions recorded on our condensed consolidated balance sheets.The following table reflects the impact of netting agreements on gross derivative assets and liabilities:As of June 30, 2016 Derivative instruments, recorded in condensed consolidated balance sheet, gross Effect of master netting agreements Derivative instruments, net  (in thousands)Asset derivatives:      Derivative instruments, at fair value $111,584 $(30,404) $81,180       Liability derivatives:      Derivative instruments, at fair value $49,654 $(30,404) $19,250       As of December 31, 2015 Derivative instruments, recorded in condensed consolidated balance sheet, gross Effect of master netting agreements Derivative instruments, net  (in thousands)Asset derivatives:      Derivative instruments, at fair value $266,046 $(1,921) $264,125       Liability derivatives:      Derivative instruments, at fair value $2,290 $(1,921) $369        |

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| - Definition
The entire disclosure for derivative instruments and hedging activities including, but not limited to, risk management strategies, non-hedging derivative instruments, assets, liabilities, revenue and expenses, and methodologies and assumptions used in determining the amounts.
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