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Long-Term Debt (Narrative) (Details) |  | 1 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 27, 2013 USD ($) | Dec. 31, 2015 USD ($) | Sep. 30, 2013 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Sep. 18, 2015 USD ($) | Jun. 04, 2015 USD ($) | May. 29, 2015 USD ($) | Apr. 21, 2015 USD ($) | Apr. 10, 2015 USD ($) | Nov. 26, 2014 USD ($) | Nov. 25, 2014 | Aug. 18, 2014 USD ($) | Apr. 23, 2014 USD ($) | Apr. 22, 2014 USD ($) | Dec. 21, 2012 USD ($) | Oct. 17, 2012 USD ($) | Oct. 09, 2012 | Mar. 31, 2011 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Unsecured Debt Issuance Restriction |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,200,000,000.0 |  |  |  |  |  |  |  |  |  |
Debt covenant ratio for EBITDAX |  |  |  |  | 3.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-tern debt |  |  | $ 951,653,000 |  |  | $ 951,653,000 |  |  |  |  | $ 10,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unamortized discount |  |  | 2,500,000 |  |  | 2,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | [1] |  | $ (12,493,000) |  |  | (12,493,000) |  | $ (14,658,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest capitalized |  |  |  |  |  | $ 13,580,000 |  | 9,687,000 |  | $ 7,132,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt covenant ratio for future EBITDAX |  |  | 4.00 |  |  | 4.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required Minimum Down Payment |  |  |  |  |  | 30.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-tern debt |  |  | $ 0 |  |  | $ 0 |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-tern debt |  |  | 1,653,000 | [2] |  | 1,653,000 | [2] | 1,826,000 | [2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,400,000
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.82%
Monthly interest and principal payments |  |  | 20,000 |  | $ 22,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest capitalized |  |  |  |  |  | 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-tern debt |  |  | 600,000,000 | [3] |  | 600,000,000 | [3] | 600,000,000 | [3] |  |  |  |  |  |  |  |  | $ 600,000,000.0 | [4] |  |  |  |  |  |
Effective interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.561% |  |  |  | 7.531% | 8.00% |  |
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% |
Discount issue price, price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 98.534% |  |
Premium issue price, percent |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 106.00% |  |  |  | 101.00% |  |  |
Unamortized discount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,700,000 |  |
Unamortized premium |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18,000,000 |  |  |  | $ 500,000 |  |  |
Senior Notes | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption of principal amount plus aggregate net proceeds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 35.00% |
Senior Notes | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of notes required to be outstanding for redemption |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 65.00% |
6.625% Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-tern debt | [4] |  | 350,000,000 |  |  | 350,000,000 |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.625% |  |  |  |  |  |  |  |  |  |  |
7.75% Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  | 7.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Credit facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 125,000,000.0 |  |  |  |  |  |  |  |  |
October Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  |  | $ 5,100,000 |  |  | $ 5,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Refinanced Building Loan | Building loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  | 4.00% |  |  | 4.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amended And Restated Credit Agreement | Construction Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 30,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |
Amended And Restated Credit Agreement | Letter of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Credit facility |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |
Fifth Amended And Restated Credit Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowing capacity |  |  |  |  |  |  |  |  |  |  | $ 700,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt covenant ratio for future EBITDAX |  |  |  |  |  |  |  |  |  |  | 4.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-tern debt |  |  |  |  |  |  |  |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt, Maximum Indebtedness, Percent |  |  |  |  |  |  |  |  |  |  | 2.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fifth Amended And Restated Credit Agreement | Letter of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Credit facility |  |  |  |  |  |  |  |  |  |  | $ 150,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line Of Credit Facility, Maximum Borrowing Capacity, Percentage Of Borrowing Base |  |  |  |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line Of Credit Facility, Borrowing Capacity Restriction, Maximum Investment In Joint Ventures |  |  |  |  |  |  |  |  |  |  | $ 100,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term Line of Credit |  |  | $ 178,600,000 |  |  | $ 178,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future borrowings available |  |  | 521,400,000 |  |  | 521,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notes Due 2023 | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 350,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.625% |  |  |  |  |  |  |  |  |  |  |
6.625% Senior Notes | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-tern debt |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 343,600,000 |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.625% |  |  |  |  |  |  |  |  |  |  |
December Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unamortized premium |  |  | 300,000 |  |  | 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  |  | 1,100,000 |  |  | 1,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
August Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unamortized premium |  |  | 14,700,000 |  |  | 14,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  |  | 4,900,000 |  |  | $ 4,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
April Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,800,000 |  |  |  |  |
Nova Scotia, Amegy, KeyBank |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Credit facility |  | $ 1,500,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowing capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 575,000,000.0 | 450,000,000.0 |  |  |  | 275,000,000.0 | $ 150,000,000.0 |  |  |  |
Debt instrument, description of rate |  |  |  |  |  | LIBOR01 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank | Letter of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowing capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 70,000,000.0 | $ 20,000,000.0 |  |  |  |
Debt covenant ratio for EBITDAX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.00 |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank | Second Amendment of Restated Credit Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowing capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 450,000,000.0 |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank | Second Amendment of Restated Credit Agreement | Letter of Credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowing capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 125,000,000.0 |  |  |  |  |  |  |  |  |
Debt covenant ratio for EBITDAX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.50 |  |  |  |  |  |  |  |  |
Debt covenant ratio for future EBITDAX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.25 |  |  |  |  |  |  |  |  |
Disposition costs, maximum expenses allowed |  |  |  |  |  | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank | Base Rate Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, minimum |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, maximum |  | 1.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank | Base Rate Loans | Federal Funds Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank | Base Rate Loans | Eurodollar |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread |  | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nova Scotia, Amegy, KeyBank | Euro Dollar Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, minimum |  | 1.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Applicable rate, maximum |  | 2.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
InterBank | Letter of Credit | Construction Loans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Credit facility |  |  |  |  |  |  |  |  |  |  |  | $ 24,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term Line of Credit |  |  | $ 0 |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  | 4.50% |  |  |  |  |  |  |  |  |  |  |  |  |
Oil and Gas Properties |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest capitalized |  |  |  |  |  | $ 13,300,000 |  | $ 9,687,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | The October Notes were issued at a price of 98.534% resulting in a gross discount of $3.7 million and an effective rate of 8.000%. The December Notes were issued at a price of 101.000% resulting in a gross premium of $0.5 million and an effective rate of 7.531%. The August Notes were issued at a price of 106.000% resulting in a gross premium of $18.0 million and an effective rate of 6.561%. The April Notes were issued at par. The premium and discount are being amortized using the effective interest method.
[2] | 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 matured in February 2016 and bore interest at the rate of 5.82% per annum. The new building loan required monthly interest and principal payments of approximately $22,000 and is collateralized by the Oklahoma City office building and associated land. Subsequently, the loan was refinanced with a new interest rate of 4.00% per annum. The building loan currently matures in December 2018 and requires monthly interest and principal payments of approximately $20,000. The Company paid the balance of the loan in full subsequent to December 31, 2015.
[3] | On October 17, 2012, the Company issued $250.0 million in aggregate principal amount of senior unsecured notes due 2020 (the "October Notes") 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") as additional securities under the senior note indenture. The Company used a portion of the net proceeds from the sale of the October Notes to repay all amounts outstanding at such time under its revolving credit facility. The Company used the remaining net proceeds from the sale of the October Notes and the net proceeds from the sale of the December Notes 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"). The August Notes were issued as additional securities under the senior note indenture. The Company used a portion of the net proceeds from the sale of the August Notes to repay all amounts outstanding at such time under its revolving credit facility. The Company used the remaining net proceeds from the sale of the August Notes for general corporate purposes, including funding a portion of its 2014 and 2015 capital development plans. The October Notes, December Notes and the August Notes are collectively referred to as the "2020 Notes".In connection with the issuance of the 2020 Notes, the Company and the subsidiary guarantors entered into registration rights agreements with the initial purchasers, pursuant to which the Company and the subsidiary guarantors agreed to file a registration statement with respect to an offer to exchange the 2020 Notes for a new issue of substantially identical debt securities registered under the Securities Act. The exchange offer for the October Notes and the December Notes was completed in October 2013 and the exchange offer for the August Note was completed in March 2015.Under the senior note indenture relating to the 2020 Notes, interest on the 2020 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 2020 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 2020 Notes; provided, however, that the 2020 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 2020 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 2020 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 2020 Notes with the net proceeds of certain equity offerings, provided that at least 65% of the aggregate principal amount of the 2020 Notes initially issued remains outstanding immediately after such redemption.
[4] | On April 21, 2015, the Company issued $350.0 million in aggregate principal amount of 6.625% Senior Notes due 2023 (the "2023 Notes" and, together with the "2020 Notes," the "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 "2023 Notes Offering"). The Company received net proceeds of approximately $343.6 million after initial purchaser discounts and commissions and estimated offering expenses.The 2023 Notes were issued under an indenture, dated as of April 21, 2015, among the Company, the subsidiary guarantors party thereto and Wells Fargo Bank, National Association, as trustee. Pursuant to the indenture relating to the 2023 Notes, interest on the 2023 Notes will accrue at a rate of 6.625% per annum on the outstanding principal amount thereof from April 21, 2015, payable semi-annually on May 1 and November 1 of each year, commencing on November 1, 2015. The 2023 Notes are not guaranteed by Grizzly Holdings, Inc. and will not be guaranteed by any of the Company's future unrestricted subsidiaries.In connection with the 2023 Notes Offering, the Company and its subsidiary guarantors entered into a registration rights agreement, dated as of April 21, 2015, pursuant to which the Company agreed to file a registration statement with respect to an offer to exchange the 2023 Notes for a new issue of substantially identical debt securities registered under the Securities Act. The exchange offer for the 2023 Notes was completed on October 13, 2015.

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