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Long-Term Debt (Narrative) (Details) |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 23, 2014 USD ($) | Mar. 31, 2011 USD ($) | Jun. 30, 2015 USD ($) | Jun. 30, 2014 USD ($) | Jun. 30, 2015 USD ($) | Jun. 30, 2014 USD ($) | Jun. 04, 2015 USD ($) | May. 29, 2015 USD ($) | Apr. 21, 2015 USD ($) | Apr. 10, 2015 USD ($) | Dec. 31, 2014 USD ($) | Nov. 26, 2014 USD ($) | Aug. 18, 2014 USD ($) | Apr. 22, 2014 USD ($) | Dec. 27, 2013 USD ($) | Dec. 21, 2012 USD ($) | Oct. 17, 2012 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest cost capitalized, undeveloped properties |  |  |  | $ 4,700,000 |  | $ 3,900,000 | $ 8,400,000 |  | $ 6,200,000 |  |  |  |  |  |  |  |  |  |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt covenant ratio for EBITDAX |  |  |  | 3.00 |  |  | 3.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt covenant ratio for future EBITDAX |  |  |  | 3.25 |  |  | 3.25 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt covenant ratio for reasonable transactions |  |  |  | 3.50 |  |  | 3.50 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building loan outstanding amount of building loan refinanced |  |  | $ 2,400,000 | $ 1,738,000 | [1] |  | $ 1,738,000 | [1] |  |  |  |  |  | $ 1,826,000 | [1] |  |  |  |  |  |
Stated interest rate |  |  | 5.82% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan, periodic payment |  |  | $ 22,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building loan outstanding amount of building loan refinanced |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 600,000,000.0 |  |  | $ 600,000,000.0 | $ 600,000,000.0
Effective interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.561% |  |  | 7.531% | 8.00%
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.75% |  |  | 7.75% | 7.75%
Discount issue price, price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 98.534%
Unamortized discount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,700,000
Premium issue price, percent |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 106.00% |  |  | 101.00% |
Unamortized premium |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18,000,000 |  |  | $ 500,000 |
Construction Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building loan outstanding amount of building loan refinanced | [2] |  |  | 0 |  |  | 0 |  |  |  |  |  |  | 0 |  |  |  |  |  |  |
7.75% Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building loan outstanding amount of building loan refinanced | [3] |  |  | 600,000,000 |  |  | 600,000,000 |  |  |  |  |  |  | $ 600,000,000 |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.75%
Debt issued |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300,000,000.0 |  |  | $ 50,000,000.0 | $ 250,000,000.0
Redemption of principal amount plus aggregate net proceeds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |
7.75% Senior Notes [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of notes required to be outstanding for redemption |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 65.00% |
7.75% Senior Notes [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption of principal amount plus aggregate net proceeds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 35.00% |
Amended And Restated Credit Agreement [Member] | Construction Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, amount |  |  |  |  |  |  |  |  |  |  | $ 30,000,000.0 |  |  |  |  |  |  |  |  |  |
6.625% Senior Notes [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building loan outstanding amount of building loan refinanced |  |  |  |  |  |  |  |  |  |  |  | $ 343,600,000 |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  | 6.625% |  |  |  |  |  |  |  |  |
Letter of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility |  |  |  |  |  |  |  |  |  |  | 125,000,000.0 |  |  |  |  |  |  |  |  |  |
Letter of Credit [Member] | Amended And Restated Credit Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility |  |  |  |  |  |  |  |  |  |  | $ 150,000,000.0 |  |  |  |  |  |  |  |  |  |
Credit facility outstanding |  |  |  | 92,700,000 |  |  | 92,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  | $ 482,300,000 |  |  | 482,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,500,000,000.0 |  |
Borrowing capacity |  | $ 275,000,000.0 |  |  |  |  |  |  |  |  |  |  | $ 575,000,000.0 |  |  | $ 450,000,000.0 |  | $ 150,000,000.0 |  |  |
Line of credit, unsecured debt issuance restriction |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,200,000,000.0 |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank [Member] | Base Rate Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, minimum |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, maximum |  | 1.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank [Member] | Base Rate Loans [Member] | Federal Funds Rate [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank [Member] | Base Rate Loans [Member] | Eurodollar [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread |  | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank [Member] | Euro Dollar Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, minimum |  | 1.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, maximum |  | 2.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank [Member] | Letter of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowing capacity |  | $ 70,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 125,000,000.0 |  | $ 20,000,000.0 |  |  |
Debt covenant ratio for EBITDAX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.00 |  |  |  |  |
Nova Scotia, Amegy, KeyBank [Member] | Letter of Credit [Member] | Second Amendment of Restated Credit Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt covenant ratio for EBITDAX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.50 |  |  |  |  |
Debt covenant ratio for future EBITDAX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.25 |  |  |  |  |
Disposition costs, maximum expenses allowed |  |  |  |  |  |  | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
InterBank [Member] | Line of Credit [Member] | Construction Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility |  |  |  |  |  |  |  |  |  | $ 24,500,000.0 |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  | 450.00% |  |  |  |  |  |  |  |  |  |  |
[1] | In March 2011, the Company entered into a new building loan agreement for the office building it occupies in Oklahoma City, Oklahoma. The new loan agreement refinanced the $2.4 million outstanding under the previous building loan agreement. The new agreement matures in February 2016 and bears interest at the rate of 5.82% per annum. The new building loan requires monthly interest and principal payments of approximately $22,000 and is collateralized by the Oklahoma City office building and associated land.
[2] | On June 4, 2015, the Company entered into a construction loan agreement (the "Construction Loan") with InterBank for the construction of a new corporate headquarters in Oklahoma City. The Construction Loan allows for a maximum principal amount of $24.5 million to be drawn. Interest accrues daily on the outstanding principal balance at a fixed rate of 4.50% per annum and is payable on the last day of the month beginning June 30, 2015 through May 31, 2017. Monthly interest and principal payments are due beginning June 30, 2017, with the final payment due June 4, 2025. As of June 30, 2015, the Company had not drawn on this loan.
[3] | On October 17, 2012, the Company issued $250.0 million in aggregate principal amount of senior unsecured notes due 2020 (the "October Notes") to qualified institutional buyers pursuant to Rule 144A under the Securities Act and to certain non-U.S. persons in accordance with Regulation S under the Securities Act (the "October Notes Offering") under an indenture among the Company, its subsidiary guarantors and Wells Fargo Bank, National Association, as the trustee (the "senior note indenture"). On December 21, 2012, the Company issued an additional $50.0 million in aggregate principal amount of senior unsecured notes due 2020 (the "December Notes") to qualified institutional buyers pursuant to Rule 144A under the Securities Act and to certain non-U.S. persons in accordance with Regulation S under the Securities Act ("the December Notes Offering"). The December Notes were issued as additional securities under the senior note indenture. The Company used a portion of the net proceeds from the October Notes Offering to repay all amounts outstanding at such time under its revolving credit facility. The Company used the remaining net proceeds of the October Notes Offering and the net proceeds of the December Notes Offering for general corporate purposes, which included funding a portion of its 2013 capital development plan. The October Notes and the December Notes were exchanged for substantially identical notes in the same aggregate principal amount that were registered under the Securities Act in October 2013 (the "Exchange Notes").On August 18, 2014, the Company issued an additional $300.0 million in aggregate principal amount of senior unsecured notes due 2020 (the "August Notes") to qualified institutional buyers pursuant to Rule 144A under the Securities Act and to certain non-U.S. persons in accordance with Regulation S under the Securities Act ("the August Notes Offering"). The August Notes were issued as additional securities under the senior note indenture. The Company used a portion of the net proceeds from the August Notes Offering to repay all amounts outstanding at such time under its revolving credit facility. The Company intends to use the remaining net proceeds of the August Notes Offering for general corporate purposes, including funding a portion of its 2014 and 2015 capital development plans. The October Notes Offering, December Notes Offering and the August Notes Offering are collectively referred to as the "Notes Offerings" and the Exchange Notes, and the August Notes are collectively referred to as the "Old Notes".In connection with the issuance of the August Notes, the Company and the subsidiary guarantors entered into a registration rights agreement with the initial purchasers on August 18, 2014, pursuant to which the Company and the subsidiary guarantors have agreed to file a registration statement with respect to an offer to exchange the August Notes for a new issue of substantially identical debt securities registered under the Securities Act. The registration statement relating to the exchange offer for the August Notes was filed on November 6, 2014, as amended on February 3, 2015, and declared effective by the SEC on February 4, 2015. The exchange offer for the August Notes was completed in March 2015.Under the senior note indenture relating to the Old Notes, interest on the Old Notes accrues at a rate of 7.75% per annum on the outstanding principal amount from October 17, 2012, payable semi-annually on May 1 and November 1 of each year, commencing on May 1, 2013. The Old Notes are the Company's senior unsecured obligations and rank equally in the right of payment with all of the Company's other senior indebtedness and senior in right of payment to any future subordinated indebtedness. All of the Company's existing and future restricted subsidiaries that guarantee the Company's secured revolving credit facility or certain other debt guarantee the Old Notes; provided, however, that the Old Notes are not guaranteed by Grizzly Holdings, Inc. and will not be guaranteed by any of the Company's future unrestricted subsidiaries. The Company may redeem some or all of the Old Notes at any time on or after November 1, 2016, at the redemption prices listed in the senior note indenture. Prior to November 1, 2016, the Company may redeem the Old Notes at a price equal to 100% of the principal amount plus a “make-whole” premium. In addition, prior to November 1, 2015, the Company may redeem up to 35% of the aggregate principal amount of the Old Notes with the net proceeds of certain equity offerings, provided that at least 65% of the aggregate principal amount of the Old Notes initially issued remains outstanding immediately after such redemption.

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