Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Change in Standard Measure of Discounted Future Net Cash Flows (Details)

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Supplemental Oil and Gas Disclosures - Change in Standard Measure of Discounted Future Net Cash Flows (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Changes in Standardized Measure      
Standardized measure, beginning of year $ 493.7 $ 986.9 $ 1,067.0
Sales and transfers of oil and gas produced, net of production costs (370.5) (168.6) (315.8)
Net changes in price, net of future production costs 980.9 (503.7) (376.4)
Extensions and discoveries, net of future production and development costs   2.8 27.0
Changes in estimated future development costs (25.4) (15.9) (6.0)
Previously estimated development costs incurred 0.6 1.4 19.3
Revisions of quantity estimates 289.6 (65.2) 116.4
Accretion of discount 44.0 111.8 107.4
Net change in income taxes (181.8) 87.7 62.9
Purchases of reserves in-place 0.5 44.6 298.3
Sales of reserves in-place 0.0 0.0  
Changes in production rates due to timing and other (75.6) 11.9 (13.2)
Net (decrease) increase 662.3 (493.2) (80.1)
Standardized measure, end of year $ 1,156.0 $ 493.7 $ 986.9