Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Effect of New Accounting Standard) (Details)

v3.10.0.1
Summary of Significant Accounting Policies (Effect of New Accounting Standard) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jan. 01, 2019
Operating revenues                        
Total operating revenues $ 161,895 $ 161,214 $ 137,075 $ 127,440 $ 118,214 $ 84,614 $ 82,283 $ 81,363 $ 587,624 $ 366,474 $ 200,851  
Operating expenses                        
Lease operating expenses                 69,180 49,907 38,353  
Total operating expenses                 328,094 225,028 248,328  
Natural gas sales                        
Operating revenues                        
Total operating revenues                 56,726 $ 44,100 $ 23,199  
Calculated under Revenue Guidance in Effect before Topic 606                        
Operating revenues                        
Total operating revenues                 595,270      
Operating expenses                        
Lease operating expenses                 76,826      
Total operating expenses                 335,740      
Calculated under Revenue Guidance in Effect before Topic 606 | Natural gas sales                        
Operating revenues                        
Total operating revenues                 64,372      
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606                        
Operating revenues                        
Total operating revenues                 7,646      
Operating expenses                        
Lease operating expenses                 7,646      
Total operating expenses                 7,646      
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Natural gas sales                        
Operating revenues                        
Total operating revenues                 $ 7,646      
Minimum | Forecast | Accounting Standards Update 2016-02                        
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]                        
Operating lease, liability                       $ 45,000
Right-of-use asset                       45,000
Maximum | Forecast | Accounting Standards Update 2016-02                        
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]                        
Operating lease, liability                       55,000
Right-of-use asset                       $ 55,000