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Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items] |  |  |
Sales and transfers of oil and gas produced, net of production costs | $ (734,354) | $ (1,063,215) | $ (756,257)
Net changes in prices, production costs, and development costs | (1,372,443) | 590,519 | 913,714
Acquisition of oil and gas reserves in place | 0 | 0 | 703,866
Extensions and discoveries | 388,151 | 519,137 | 618,039
Previously estimated development costs incurred during the period | 405,979 | 402,156 | 390,673
Revisions of previous quantity estimates, less related production costs | (321,397) | (356,933) | 155,200
Sales of oil and gas reserves in place | (48,547) | (25,882) | 0
Accretion of discount | 298,273 | 264,356 | 68,804
Net changes in income taxes | 424,628 | (185,157) | (231,545)
Change in production rates and other | (319,428) | 194,180 | 93,030
Total change in standardized measure of discounted future net cash flows | (1,279,138) | 339,161 | 1,955,524
Investment in Grizzly Oil Sands ULC |  |  |
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items] |  |  |
Sales and transfers of oil and gas produced, net of production costs | 0 | 0 | 0
Net changes in prices, production costs, and development costs | 0 | 0 | 0
Acquisition of oil and gas reserves in place | 0 | 0 | 0
Extensions and discoveries | 0 | 0 | 0
Previously estimated development costs incurred during the period | 0 | 0 | 0
Revisions of previous quantity estimates, less related production costs | 0 | 0 | 0
Accretion of discount | 0 | 0 | 0
Net changes in income taxes | 0 | 0 | 0
Change in production rates and other | 0 | 0 | 0
Total change in standardized measure of discounted future net cash flows | $ 0 | $ 0 | $ 0

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- Definition Net change in sales and transfer prices and in production (lifting) costs related to future production and in the evaluation of the costs that will be required in future periods to make it possible to extract or process proved oil and gas reserves. + References No definition available. + Details
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