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Fair Value Measurements - Additional Information (Details)
$ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2019
USD ($)
Dec. 31, 2020
USD ($)
Swap
Dec. 31, 2019
USD ($)
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]      
Estimated fair value of derivative instruments, net liability   $ 51.2  
Derivative fair value of net liability if commodity price increases by 10 percent   (158.5)  
Derivative fair value of net asset if commodity price decreases by 10 percent   $ 56.4  
Number of natural gas basis swaps categorized as Level 3 | Swap   1  
Non-cash pre-tax impairments $ 225.3 $ 2,442.8 $ 225.3