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Supplemental Gas Data (unaudited) - Proved Undeveloped Reserves (Details)
bbl in Thousands, Mcfe in Thousands, Mcf in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2020
USD ($)
Mcfe
well
Mcf
bbl
Dec. 31, 2019
USD ($)
Mcfe
bbl
Mcf
Dec. 31, 2018
USD ($)
Mcfe
Mcf
bbl
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Beginning balance (energy) 8,425,667 7,881,335 7,581,612
Revisions (energy) 740,129 (518,570) 320,925
Price changes (energy) (1,351,934) (45,246) 28,315
Extensions and Discoveries (energy) 2,246,968 1,647,297 960,808
Production (MMcfe) (511,072) (539,149) (507,104)
Sales of Reserves In-Place (energy)     (825,196)
Ending balance (energy) 9,549,758 8,425,667 7,881,335
Proved developed resources (energy) 5,199,748 4,838,858 4,494,878
Proved undeveloped resources (energy) 4,350,010 3,586,809 3,386,457
Upward revision from increased performance (energy) 579,000 657,000 472,000
Downward revision due to plan changes (energy) 677,000 872,000 151,000
Proved and unproved resources, extensions and discoveries (energy) 70,000 77,000  
Downward revision due to PUD removal (energy)   304,000  
Increase in reserve due to decrease in operating costs (energy) 853,000    
Capital spent related to undeveloped reserves transferred to developed | $ $ 487,291 $ 1,192,599 $ 1,116,397
Reserves reported for more than five years 320,987    
Utica      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Downward revision due to plan changes (energy) 88,000    
Number of wells removed from development plan | well 4    
Utica | Central Pennsylvania and Southwest Pennsylvania      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved and unproved resources, extensions and discoveries (energy) 711,000    
Number of dry gas wells added | well 23    
Marcellus      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Upward revision from increased performance (energy) 342,000    
Downward revision due to plan changes (energy) 579,000    
Number of wells removed from development plan | well 23    
Marcellus | Southwest Pennsylvania and West Virginia      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved and unproved resources, extensions and discoveries (energy) 1,465,000    
Number of dry gas wells added | well 47    
Natural Gas      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning balance (volume) | Mcf 7,938,406 7,436,338 7,121,758
Revisions (volume) | Mcf 407,836 (521,617) 313,091
Price Changes (volume) | Mcf (1,019,523) (40,773) 28,100
Extension and Discoveries (volume) | Mcf 2,188,773 1,569,813 839,268
Production (volume) | Mcf (481,426) (505,355) (468,228)
Sales of Reserves In-Place (volume) | Mcf     (715,088)
Ending balance (volume) | Mcf 9,034,066 7,938,406 7,436,338
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved developed resources (volume) | Mcf 4,939,283 4,473,534 4,242,579
Proved undeveloped resources (volume) | Mcf 4,094,783 3,464,873 3,193,759
NGLs      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning balance (volume) | bbl 75,844,000 65,904,000 71,691,000
Revisions (volume) | bbl 51,857,000 5,926,000 441,000
Price Changes (volume) | bbl (50,456,000) (740,000) 32,000
Extension and Discoveries (volume) | bbl 9,299,000 10,182,000 16,247,000
Production (volume) | bbl (4,677,000) (5,428,000) (6,011,000)
Sales of Reserves In-Place (volume) | bbl     (17,252,000)
Ending balance (volume) | bbl 81,867,000 75,844,000 65,904,000
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved developed resources (volume) | bbl 42,204,000 59,800,000 40,180,000
Proved undeveloped resources (volume) | bbl 39,664,000 16,044,000 25,724,000
Condensate & Crude Oil      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning balance (volume) | bbl 5,366,000 8,261,000 4,950,000
Revisions (volume) | bbl 3,525,000 (5,418,000) 865,000
Price Changes (volume) | bbl (4,946,000) (5,000) 4,000
Extension and Discoveries (volume) | bbl 400,000 2,732,000 4,010,000
Production (volume) | bbl (264,000) (204,000) (468,000)
Sales of Reserves In-Place (volume) | bbl     (1,100,000)
Ending balance (volume) | bbl 4,081,000 5,366,000 8,261,000
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved developed resources (volume) | bbl 1,207,000 1,087,000 1,870,000
Proved undeveloped resources (volume) | bbl 2,874,000 4,278,000 6,391,000
Proved Undeveloped      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Beginning balance (energy) 3,586,809    
Undeveloped reserves transferred to developed (1,152,598)    
Extensions and Discoveries (energy) 2,176,326    
Ending balance (energy) 4,350,010 3,586,809  
Capital spent related to undeveloped reserves transferred to developed | $ $ 257,952    
Proved Undeveloped | Price Revisions      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Revisions (energy) (380,200)    
Proved Undeveloped | Revisions Due to Plan Changes      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Revisions (energy) (691,054)    
Proved Undeveloped | Revisions Due to Changes Due to Well Performance      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Revisions (energy) 810,727