Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Narrative) (Details)

v3.8.0.1
Summary of Significant Accounting Policies (Narrative) (Details)
$ in Thousands
3 Months Ended 12 Months Ended
Jun. 30, 2016
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2017
USD ($)
$ / bbl
$ / MMBTU
Dec. 31, 2016
USD ($)
$ / bbl
$ / MMBTU
Dec. 31, 2015
USD ($)
Accounting Policies [Line Items]          
Discounted present value of estimated future net cash flows from proved oil and natural gas reserves     10.00%    
Write-down of oil and natural gas properties $ 61,012 $ 34,776 $ 0 $ 95,788 $ 208,435
Capitalized interest     33,783 19,857 10,459
Amortization of financing costs     2,150 3,115 3,123
Valuation allowance     $ 60,919 140,192  
Stock options          
Accounting Policies [Line Items]          
Vesting period     3 years    
RSU equity awards          
Accounting Policies [Line Items]          
Vesting period     3 years    
Cash-settleable RSU awards          
Accounting Policies [Line Items]          
Vesting period     3 years    
Other Property and Equipment [Member]          
Accounting Policies [Line Items]          
Depreciation     $ 900 793 $ 865
Accumulated depreciation     $ 16,259 $ 15,227  
Other Property and Equipment [Member] | Minimum          
Accounting Policies [Line Items]          
Estimated useful lives of other property and equipment     3 years    
Other Property and Equipment [Member] | Maximum          
Accounting Policies [Line Items]          
Estimated useful lives of other property and equipment     20 years    
Oil          
Accounting Policies [Line Items]          
Prices used in determining estimated future net cash flows from proved reserves | $ / MMBTU     51.34 42.75  
Natural gas          
Accounting Policies [Line Items]          
Prices used in determining estimated future net cash flows from proved reserves | $ / bbl     2.98 2.48