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Basis of Presentation (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Share-Based Payments          
Stock-based compensation expense $ 770 $ 807 $ 1,749 $ 1,643  
Discount rate used in future net cash flows relating to proved oil and gas reserves (percent)     10.00%    
Proved property impairment 0 28,735 $ 0 63,820  
Entity's asset retirement obligation transactions [Roll Forward]          
Beginning future site restoration obligation     8,623    
New wells placed on production and other     102   $ 119
Deletions related to property disposals and plugging costs     (77)   (1,832)
Accretion expense     224 270 491
Revisions and other     (33)   166
Ending future site restoration obligation $ 8,839   $ 8,839   $ 8,623
Employee Stock Option [Member]          
Number of Shares (thousands)          
Outstanding, December 31, 2016     8,154    
Granted     207    
Exercised     (5)    
Cancelled     (2)    
Outstanding, June 30, 2017 8,354   8,354   8,154
Weighted Average Option Exercise Price Per Share          
Outstanding, December 31, 2016     $ 2.39    
Granted     1.88    
Exercised     0.97    
Cancelled/Forfeited     3.01    
Outstanding, June 30, 2017 $ 2.38   2.38   $ 2.39
Weighted Average Grant Date Fair Value Per Share          
Outstanding, December 31, 2016     1.70    
Granted     1.23    
Exercised     0.65    
Cancelled     2.14    
Outstanding, June 30, 2017 $ 1.69   $ 1.69   $ 1.70
Share-Based Payments          
Stock-based compensation expense $ 635 479 $ 1,069 936  
Unamortized compensation cost expected to be recognized in 2016 through 2020 $ 2,200   $ 2,200    
Restricted Stock [Member]          
Number of Shares (thousands)          
Unvested, December 31, 2016     1,492    
Granted     4    
Vested/Released     (2)    
Forfeited     (1)    
Unvested, June 30, 2017 1,493   1,493   1,492
Weighted Average Grant Date Fair Value Per Share (in US$ per share)          
Unvested, December 31, 2016     $ 3.47    
Granted     2.06    
Vested/Released     3.25    
Forfeited     2.63    
Unvested, June 30, 2017 $ 3.46   $ 3.46   $ 3.47
Share-Based Payments          
Stock-based compensation expense $ 344 $ 356 $ 680 $ 707  
Unamortized compensation cost expected to be recognized in 2016 through 2020 $ 1,300   $ 1,300