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Fair Value Measurements (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Aug. 20, 2018 | Sep. 12, 2016 | May 21, 2015 | Nov. 17, 2014 | May 20, 2013
Assets: |  |  |  |  |  |  |  |  |  |
Derivative Assets, Fair Value, Gross Asset | $ 233,629 |  | $ 104,628 |  |  |  |  |  |  |
Liabilities: |  |  |  |  |  |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability | 75,349 |  | 243,984 |  |  |  |  |  |  |
Proved Oil and Gas Properties |  |  |  |  |  |  |  |  |  |
Impairment of proved properties | 0 |  | 3,806 |  | $ 354,614 |  |  |  |  |
Abandonment and impairment of unproved properties | $ 49,889 |  | 12,272 |  | $ 80,367 |  |  |  |  |
6.50% Senior Notes Due 2021 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 6.50% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 0 |  | 344,611 |  |  |  |  |  |  |
Long-term Debt, Fair Value | $ 0 |  | 351,682 |  |  |  |  |  |  |
6.125% Senior Notes Due 2022 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 6.125% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 476,796 |  | 561,796 |  |  |  |  |  | $ 600,000 |
Long-term Debt, Fair Value | $ 452,336 |  | 571,627 |  |  |  |  |  |  |
6.50% Senior Notes Due 2023 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 6.50% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 0 |  | 394,985 |  |  |  |  |  |  |
Long-term Debt, Fair Value | $ 0 |  | 403,434 |  |  |  |  |  |  |
5% Senior Notes Due 2024 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 5.00% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 500,000 |  | 500,000 |  |  |  |  |  |  | $ 500,000
Long-term Debt, Fair Value | $ 439,265 |  | 483,440 |  |  |  |  |  |  |
5.625% Senior Notes Due 2025 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 5.625% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 500,000 |  | 500,000 |  |  |  |  | $ 500,000 |  |
Long-term Debt, Fair Value | $ 436,460 |  | 494,355 |  |  |  |  |  |  |
6.75% Senior Notes Due 2026 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 6.75% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 500,000 |  | 500,000 |  |  |  | $ 500,000 |  |  |
Long-term Debt, Fair Value | $ 448,305 |  | 516,350 |  |  |  |  |  |  |
6.625% Senior Notes Due 2027 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 6.625% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 500,000 |  | 0 |  |  | $ 500,000 |  |  |  |
Long-term Debt, Fair Value | $ 442,500 |  | 0 |  |  |  |  |  |  |
1.50% Senior Convertible Notes Due 2021 [Domain] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Fair Value Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage | 1.50% |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount | $ 172,500 |  | 172,500 |  |  |  |  |  |  |
Long-term Debt, Fair Value | 158,614 |  | 168,291 |  |  |  |  |  |  |
Not Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |
Derivative Assets, Fair Value, Gross Asset | 0 | [1] | 0 | [2] |  |  |  |  |  |
Liabilities: |  |  |  |  |  |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability | 0 | [1] | 0 | [2] |  |  |  |  |  |
Not Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |
Derivative Assets, Fair Value, Gross Asset | 233,629 | [1] | 104,628 | [2] |  |  |  |  |  |
Liabilities: |  |  |  |  |  |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability | 75,349 | [1] | 243,984 | [2] |  |  |  |  |  |
Not Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |
Derivative Assets, Fair Value, Gross Asset | 0 | [1] | 0 | [2] |  |  |  |  |  |
Liabilities: |  |  |  |  |  |  |  |  |  |
Derivative Liability, Fair Value, Gross Liability | $ 0 | [1] | $ 0 | [2] |  |  |  |  |  |
[1] | (1) This represents a financial asset or liability that is measured at fair value on a recurring basis.
[2] | (1) This represents a financial asset or liability that is measured at fair value on a recurring basis.

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