Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Narrative) (Details)

v3.10.0.1
Summary of Significant Accounting Policies (Narrative) (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
$ / bbl
$ / MMBTU
Dec. 31, 2017
USD ($)
$ / bbl
$ / MMBTU
Dec. 31, 2016
USD ($)
$ / bbl
$ / MMBTU
Accounting Policies [Line Items]      
Write-down of oil and natural gas properties $ 0 $ 0 $ 95,788,000
Capitalized interest 56,151,000 33,783,000 19,857,000
Amortization of financing costs 2,483,000 2,150,000 3,115,000
Valuation allowance $ 0 60,919,000  
Stock options      
Accounting Policies [Line Items]      
Vesting period 3 years    
RSU equity awards | Employees      
Accounting Policies [Line Items]      
Vesting period 3 years    
RSU equity awards | Directors      
Accounting Policies [Line Items]      
Vesting period 1 year    
Cash-settleable RSU awards      
Accounting Policies [Line Items]      
Vesting period 3 years    
Other Property and Equipment      
Accounting Policies [Line Items]      
Depreciation $ 1,078,000 900,000 $ 793,000
Accumulated depreciation $ 16,562,000 $ 16,259,000  
Other Property and Equipment | Minimum      
Accounting Policies [Line Items]      
Estimated useful lives of other property and equipment 3 years    
Other Property and Equipment | 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 58.40 51.34 42.75
Natural gas      
Accounting Policies [Line Items]      
Prices used in determining estimated future net cash flows from proved reserves | $ / bbl 3.64 2.98 2.48