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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, 2019
USD ($)
well
Mcfe
Mcf
bbl
Dec. 31, 2018
USD ($)
Mcfe
Mcf
bbl
Dec. 31, 2017
USD ($)
Mcfe
Mcf
bbl
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Beginning balance (energy) 7,881,335 7,581,612 6,251,648
Revisions (energy) (518,570) 320,925 (232,321)
Price changes (energy) (45,246) 28,315 181,470
Extensions and Discoveries (energy) 1,647,297 960,808 1,887,153
Production (MMcfe) (539,149) (507,104) (407,166)
Purchases of Reserves In-Place (energy)   321,975  
Sales of Reserves In-Place (energy)   (825,196) (99,172)
Ending balance (energy) 8,425,667 7,881,335 7,581,612
Proved developed resources (energy) 4,838,858 4,494,878 4,409,065
Proved undeveloped resources (energy) 3,586,809 3,386,457 3,172,547
Downward revision due to PUD removal (energy) (304,000)   (458,000)
Upward revision from increased performance through optimization (energy) 657,000 472,000  
Downward revision due to plan changes (energy) 872,000 151,000  
Capital spent related to undeveloped reserves transferred to developed | $ $ 1,192,599 $ 1,116,397 $ 632,846
Reserves reported for more than five years 248,570    
Number of wells pending determination of proved reserves | well 1    
Proved Undeveloped      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Capital spent related to undeveloped reserves transferred to developed | $ $ 334,062    
Proved Undeveloped      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Beginning balance (energy) 3,386,457    
Undeveloped reserves transferred to developed (752,970)    
Extensions and Discoveries (energy) 1,570,576    
Ending balance (energy) 3,586,809 3,386,457  
Proved Undeveloped | Revisions Due to Five Year Rule      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Revisions (energy) (303,787)    
Proved Undeveloped | Price Revisions      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Revisions (energy) 2,147    
Proved Undeveloped | Revisions Due to Plan Changes      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Revisions (energy) (872,495)    
Proved Undeveloped | Revisions Due to Changes Due to Well Performance      
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Revisions (energy) 556,881    
Natural Gas      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning balance (volume) | Mcf 7,436,338 7,121,758 5,828,399
Revisions (volume) | Mcf (521,617) 313,091 (202,735)
Price Changes (volume) | Mcf (40,773) 28,100 173,738
Extension and Discoveries (volume) | Mcf 1,569,813 839,268 1,769,029
Production (volume) | Mcf (505,355) (468,228) (364,893)
Purchases of Reserves In-Place (volume) | Mcf   317,437  
Sales of Reserves In-Place (volume) | Mcf   (715,088) (81,780)
Ending balance (volume) | Mcf 7,938,406 7,436,338 7,121,758
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved developed resources (volume) | Mcf 4,473,534 4,242,579 4,051,526
Proved undeveloped resources (volume) | Mcf 3,464,873 3,193,759 3,070,232
NGLs      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning balance (volume) | bbl 65,904,000 71,691,000 60,532,000
Revisions (volume) | bbl 5,926,000 441,000 1,162,000
Price Changes (volume) | bbl (740,000) 32,000 1,188,000
Extension and Discoveries (volume) | bbl 10,182,000 16,247,000 17,887,000
Production (volume) | bbl (5,428,000) (6,011,000) (6,456,000)
Purchases of Reserves In-Place (volume) | bbl   756,000  
Sales of Reserves In-Place (volume) | bbl   (17,252,000) (2,622,000)
Ending balance (volume) | bbl 75,844,000 65,904,000 71,691,000
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved developed resources (volume) | bbl 59,800,000 40,180,000 56,022,000
Proved undeveloped resources (volume) | bbl 16,044,000 25,724,000 15,669,000
Condensate & Crude Oil      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning balance (volume) | bbl 8,261,000 4,950,000 10,009,000
Revisions (volume) | bbl (5,418,000) 865,000 (5,834,000)
Price Changes (volume) | bbl (5,000) 4,000 (159,000)
Extension and Discoveries (volume) | bbl 2,732,000 4,010,000 1,800,000
Production (volume) | bbl (204,000) (468,000) (589,000)
Purchases of Reserves In-Place (volume) | bbl   0  
Sales of Reserves In-Place (volume) | bbl   (1,100,000) (277,000)
Ending balance (volume) | bbl 5,366,000 8,261,000 4,950,000
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]      
Proved developed resources (volume) | bbl 1,087,000 1,870,000 3,567,000
Proved undeveloped resources (volume) | bbl 4,278,000 6,391,000 1,383,000