Annual report pursuant to Section 13 and 15(d)

Acquisitions and Dispositions (Narrative) (Details)

v3.10.0.1
Acquisitions and Dispositions (Narrative) (Details)
$ / shares in Units, shares in Millions
3 Months Ended 12 Months Ended
Aug. 31, 2018
USD ($)
a
Jun. 05, 2017
USD ($)
a
Feb. 13, 2017
USD ($)
a
Oct. 20, 2016
USD ($)
a
May 26, 2016
USD ($)
a
$ / shares
shares
Dec. 31, 2018
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
May 19, 2017
USD ($)
Oct. 03, 2016
USD ($)
Business Acquisition [Line Items]                        
Acquisition deposit           $ 0   $ 0 $ 900,000      
Proceeds from sales of working interest               $ 9,009,000 $ 20,525,000 $ 24,562,000    
6.125% senior unsecured notes due 2024                        
Business Acquisition [Line Items]                        
Debt instrument principal amount                     $ 200,000,000 $ 400,000,000
Debt instrument, interest rate, stated (as a percent)           6.125%   6.125%     6.125% 6.125%
Cimarex Energy Company                        
Business Acquisition [Line Items]                        
Gas and oil area, developed and undeveloped, net | a 28,000                      
Consideration transferred $ 539,519,000                      
Monarch and Wildhorse                        
Business Acquisition [Line Items]                        
Consideration transferred             $ 37,770,000          
Wildhorse and Spur                        
Business Acquisition [Line Items]                        
Consideration transferred           $ 87,865,000            
Delaware Basin                        
Business Acquisition [Line Items]                        
Gas and oil area, developed and undeveloped, net | a   2,488 16,688                  
Consideration transferred   $ 52,014,000 $ 646,559,000                  
Gas and oil area, developed and undeveloped, gross | a   7,031 29,175                  
Working interest     82.00%                  
Net revenue interest     75.00%                  
Acquisition deposit                   46,138,000    
Plymouth Transaction                        
Business Acquisition [Line Items]                        
Gas and oil area, developed and undeveloped, net | a       5,952                
Consideration transferred       $ 339,687,000                
Gas and oil area, developed and undeveloped, gross | a       6,904                
Working interest       82.00%                
Net revenue interest       62.00%                
Big Star Transaction                        
Business Acquisition [Line Items]                        
Gas and oil area, developed and undeveloped, net | a         14,089              
Consideration transferred       $ 329,573,000 $ 220,000,000              
Gas and oil area, developed and undeveloped, gross | a         17,298              
Working interest       81.00%                
Net revenue interest       61.00%                
Shares of common stock issued in acquisition (in shares) | shares         9.3              
Sales price of common stock (usd per share) | $ / shares         $ 11.74              
Midland Basin                        
Business Acquisition [Line Items]                        
Consideration transferred                   73,240,000    
Proceeds from sales of working interest                   $ 23,045,000