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Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Tables) | 12 Months Ended
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Dec. 31, 2020
Extractive Industries [Abstract] |
Schedule of capitalized costs related to oil and gas producing activities | Capitalized Costs Related to Oil and Gas Producing Activities
| 2020 |  | 2019
| (In thousands)
Proved properties | $ | 9,359,866 |  |  | $ | 8,909,069 |
Unproved properties | 1,457,043 |  |  | 1,686,666 |
| 10,816,909 |  |  | 10,595,735 |
Accumulated depreciation, depletion, amortization and impairment | (8,778,759) |  |  | (7,191,957) |
Net capitalized costs | $ | 2,038,150 |  |  | $ | 3,403,778 |
Schedule of cost incurred in oil and gas property acquisition and development activities | Costs Incurred in Oil and Gas Property Acquisition and Development Activities
| 2020 |  | 2019 |  | 2018
| (In thousands)
Acquisition | $ | 15,260 |  |  | $ | 37,598 |  |  | $ | 119,444 |
Development | 276,622 |  |  | 594,673 |  |  | 714,269 |
Exploratory | — |  |  | 9,762 |  |  | 22,081 |
Total | $ | 291,882 |  |  | $ | 642,033 |  |  | $ | 855,794 |
Schedule of results of operations for oil and gas production activities | The results of operations exclude general office overhead and interest expense attributable to oil and gas production.
| 2020 |  | 2019 |  | 2018
| (In thousands)
Revenues | $ | 801,251 |  |  | $ | 1,354,766 |  |  | $ | 1,675,180 |
Production costs | (537,609) |  |  | (620,412) |  |  | (611,965) |
Depletion | (229,702) |  |  | (539,379) |  |  | (476,517) |
Impairment | (1,357,099) |  |  | (2,039,770) |  |  | — |
Income tax (expense) benefit | (7,290) |  |  | 7,563 |  |  | 68 |
Results of operations from producing activities | $ | (1,330,449) |  |  | $ | (1,837,232) |  |  | $ | 586,766 |
Depletion per Mcf of gas equivalent (Mcfe) | $ | 0.61 |  |  | $ | 1.08 |  |  | $ | 0.96 |
Schedule of oil and gas reserves | These estimates are reviewed annually and revised, either upward or downward, as warranted by additional performance data.
| Oil (MMBbl) |  | Natural Gas (Bcf) |  | NGL (MMBbl) |  | Natural Gas Equivalent (Bcfe)
Proved Reserves |  |  |  |  |  |  |
December 31, 2017 | 19 |  |  | 4,825 |  |  | 76 |  |  | 5,395 |
Purchases of reserves | — |  |  | — |  |  | — |  |  | — |
Extensions and discoveries | 5 |  |  | 622 |  |  | 10 |  |  | 711 |
Sales of reserves | — |  |  | (43) |  |  | — |  |  | (45) |
Revisions of prior reserve estimates | — |  |  | (827) |  |  | 1 |  |  | (821) |
Current production | (3) |  |  | (444) |  |  | (6) |  |  | (497) |
December 31, 2018 | 21 |  |  | 4,134 |  |  | 81 |  |  | 4,743 |
Purchases of reserves | — |  |  | — |  |  | — |  |  | — |
Extensions and discoveries | 4 |  |  | 997 |  |  | 13 |  |  | 1,097 |
Sales of reserves | (2) |  |  | (63) |  |  | — |  |  | (77) |
Revisions of prior reserve estimates | (2) |  |  | (562) |  |  | (27) |  |  | (734) |
Current production | (2) |  |  | (458) |  |  | (5) |  |  | (502) |
December 31, 2019 | 18 |  |  | 4,048 |  |  | 62 |  |  | 4,528 |
Purchases of reserves | — |  |  | — |  |  | — |  |  | — |
Extensions and discoveries | 1 |  |  | 216 |  |  | 3 |  |  | 240 |
Sales of reserves | — |  |  | (74) |  |  | — |  |  | (75) |
Revisions of prior reserve estimates | (4) |  |  | (1,564) |  |  | (23) |  |  | (1,725) |
Current production | (2) |  |  | (345) |  |  | (4) |  |  | (380) |
December 31, 2020 | 13 |  |  | 2,281 |  |  | 38 |  |  | 2,588 |
Proved developed reserves |  |  |  |  |  |  |
December 31, 2018 | 10 |  |  | 1,813 |  |  | 41 |  |  | 2,115 |
December 31, 2019 | 8 |  |  | 1,757 |  |  | 30 |  |  | 1,984 |
December 31, 2020 | 7 |  |  | 1,358 |  |  | 22 |  |  | 1,527 |
Proved undeveloped reserves |  |  |  |  |  |  |
December 31, 2018 | 11 |  |  | 2,321 |  |  | 40 |  |  | 2,628 |
December 31, 2019 | 10 |  |  | 2,291 |  |  | 32 |  |  | 2,544 |
December 31, 2020 | 7 |  |  | 923 |  |  | 16 |  |  | 1,061 |
Totals may not sum or recalculate due to rounding. |  |  |  |  |  |  |
Schedule of standardized measure of discounted future net cash flows relating to proved oil and gas reserves | Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves
| Year ended December 31,
| 2020 |  | 2019 |  | 2018
| (In millions)
Future cash flows | $ | 4,079 |  |  | $ | 10,451 |  |  | $ | 14,483 |
Future development and abandonment costs | (652) |  |  | (2,058) |  |  | (2,438) |
Future production costs | (2,325) |  |  | (4,513) |  |  | (5,068) |
Future production taxes | (137) |  |  | (333) |  |  | (456) |
Future income taxes | — |  |  | — |  |  | (943) |
Future net cash flows | 965 |  |  | 3,547 |  |  | 5,578 |
10% discount to reflect timing of cash flows | (425) |  |  | (1,844) |  |  | (2,596) |
Standardized measure of discounted future net cash flows | $ | 540 |  |  | $ | 1,703 |  |  | $ | 2,982 |
Schedule of changes in standardized measure of discounted future net cash flows relating to proved oil and gas reserves | Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves
| Year ended December 31,
| 2020 |  | 2019 |  | 2018
| (In millions)
Sales and transfers of oil and gas produced, net of production costs | $ | (264) |  |  | $ | (734) |  |  | $ | (1,063) |
Net changes in prices, production costs, and development costs | (954) |  |  | (1,372) |  |  | 591 |
Acquisition of oil and gas reserves in place | — |  |  | — |  |  | — |
Extensions and discoveries | 38 |  |  | 388 |  |  | 519 |
Previously estimated development costs incurred during the period | 215 |  |  | 406 |  |  | 402 |
Revisions of previous quantity estimates, less related production costs | (255) |  |  | (321) |  |  | (357) |
Sales of oil and gas reserves in place | (6) |  |  | (49) |  |  | (26) |
Accretion of discount | 170 |  |  | 298 |  |  | 264 |
Net changes in income taxes | — |  |  | 425 |  |  | (185) |
Change in production rates and other | (109) |  |  | (319) |  |  | 194 |
Total change in standardized measure of discounted future net cash flows | $ | (1,165) |  |  | $ | (1,278) |  |  | $ | 339 |

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