Annual report pursuant to Section 13 and 15(d)

Acquisitions and Dispositions (Narrative) (Details)

v3.6.0.2
Acquisitions and Dispositions (Narrative) (Details)
$ / shares in Units, $ in Thousands
 12 Months Ended
Feb. 13, 2017
USD ($)
a
Oct. 20, 2016
USD ($)
a
May 26, 2016
USD ($)
a
$ / shares
shares
Oct. 08, 2014
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Business Acquisition [Line Items]              
Proceeds from sales of working interest         $ 24,562 $ 377 $ 2,978
Acquisition deposit         46,138    
Central Midland Basin Transaction [Member]              
Business Acquisition [Line Items]              
Aggregate purchase price       $ 210,205      
October 8, 2014 Acquisitions [Member] | Central Midland Basin Transaction [Member]              
Business Acquisition [Line Items]              
Aggregate purchase price       $ 210,205      
Working interest       62.00%      
Net revenue interest       46.50%      
Net proceeds from an equity offering       $ 122,450      
Howard County, Texas [Member] | Big Star Transaction [Member]              
Business Acquisition [Line Items]              
Aggregate purchase price     $ 329,573        
Howard County, Texas [Member] | Plymouth Transaction [Member]              
Business Acquisition [Line Items]              
Aggregate purchase price   $ 339,687          
Howard County, Texas [Member] | May 26, 2016 Acquisitions [Member] | Big Star Transaction [Member]              
Business Acquisition [Line Items]              
Consideration transferred     220,000        
Aggregate purchase price     $ 329,573        
Shares of common stock issued in acquisition | shares     9,333,333        
Sales price of common stock | $ / shares     $ 11.74        
Gas and oil area, developed and undeveloped, gross | a     17,298        
Gas and oil area, developed and undeveloped, net | a     14,089        
Working interest     81.00%        
Net revenue interest     61.00%        
Howard County, Texas [Member] | October 20, 2016 Acquisitions [Member] | Plymouth Transaction [Member]              
Business Acquisition [Line Items]              
Consideration transferred   $ 339,687          
Gas and oil area, developed and undeveloped, gross | a   6,904          
Gas and oil area, developed and undeveloped, net | a   5,952          
Working interest   82.00%          
Net revenue interest   62.00%          
Central Midland Basin [Member]              
Business Acquisition [Line Items]              
Aggregate purchase price         73,240 $ 29,800 $ 8,200
Proceeds from sales of working interest         23,045    
Ward And Pecos Counties, Texas [Member] | Ameredev Transaction [Member]              
Business Acquisition [Line Items]              
Acquisition deposit         $ 46,138    
Ward And Pecos Counties, Texas [Member] | Ameredev Transaction [Member] | Subsequent Event [Member]              
Business Acquisition [Line Items]              
Consideration transferred $ 633,000            
Gas and oil area, developed and undeveloped, gross | a 27,552            
Gas and oil area, developed and undeveloped, net | a 16,688            
Working interest 82.00%            
Net revenue interest 75.00%