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Credit Facility - Narrative (Details) - USD ($)
12 Months Ended
Oct. 31, 2018
Oct. 31, 2016
Dec. 31, 2019
Oct. 23, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
May 04, 2018
May 03, 2018
Mar. 31, 2018
Line Of Credit Facility [Line Items]                          
Credit facility     $ 394,000,000   $ 413,000,000 $ 436,000,000 $ 435,000,000 $ 410,000,000 $ 402,000,000 $ 421,000,000     $ 436,000,000
Senior Line of Credit                          
Line Of Credit Facility [Line Items]                          
Maximum borrowing capacity     $ 1,000,000,000.0                    
Weighted average interest rate (percent)     4.05%         4.76%          
Credit facility     $ 394,000,000.0         $ 410,000,000.0          
Unused portion of current borrowing base     $ 256,000,000.0         $ 265,000,000.0          
Senior Line of Credit | Borrowing Base Utilization Percentage Less Than 50%                          
Line Of Credit Facility [Line Items]                          
Commitment fee payable rate (percent)     0.375%                    
Senior Line of Credit | Borrowing Base Utilization Percentage Equal to or Greater Than 50%                          
Line Of Credit Facility [Line Items]                          
Commitment fee payable rate (percent)     0.50%                    
Senior Line of Credit | Minimum                          
Line Of Credit Facility [Line Items]                          
Current ratio     1.0                    
Senior Line of Credit | Maximum                          
Line Of Credit Facility [Line Items]                          
Ratio of total debt to EBITDAX     3.5                    
Senior Line of Credit | Revolving Credit Facility                          
Line Of Credit Facility [Line Items]                          
Borrowing base $ 675,000,000.0     $ 650,000,000.0             $ 600,000,000.0 $ 550,000,000.0  
Borrowing base threshold (percent)     50.00%                    
Senior Line of Credit | Revolving Credit Facility | LIBOR Plus Margin Rate                          
Line Of Credit Facility [Line Items]                          
Interest rate (percent) 1.00%                        
Senior Line of Credit | Revolving Credit Facility | Prime Rate Plus Margin Rate                          
Line Of Credit Facility [Line Items]                          
Interest rate (percent) 0.50%                        
Senior Line of Credit | Revolving Credit Facility | Minimum | LIBOR Plus Margin Rate                          
Line Of Credit Facility [Line Items]                          
Interest rate (percent) 1.75% 2.00%                      
Senior Line of Credit | Revolving Credit Facility | Minimum | Prime Rate Plus Margin Rate                          
Line Of Credit Facility [Line Items]                          
Interest rate (percent) 0.75% 1.00%                      
Senior Line of Credit | Revolving Credit Facility | Maximum | LIBOR Plus Margin Rate                          
Line Of Credit Facility [Line Items]                          
Interest rate (percent) 2.75% 3.00%                      
Senior Line of Credit | Revolving Credit Facility | Maximum | Prime Rate Plus Margin Rate                          
Line Of Credit Facility [Line Items]                          
Interest rate (percent) 1.75% 2.00%