Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Narrative) (Details)

v3.19.3.a.u2
Summary of Significant Accounting Policies (Narrative) (Details)
 12 Months Ended
Dec. 31, 2019
USD ($)
segment
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Accounting Policies [Line Items]      
Computation of proved reserves, discount factor as percent 10.00%    
Write-down of oil and natural gas properties $ 0 $ 0 $ 0
Accumulated depreciation 31,949,000 16,562,000  
Amortization of financing costs 2,907,000 2,483,000 2,150,000
Valuation allowance $ 0 0  
Number of operating segments | segment 1    
Operating lease, liability $ 79,946,000    
Operating lease right-of-use assets $ 63,908,000    
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    
Minimum | Cash-settled SARs      
Accounting Policies [Line Items]      
Expiration period 1 year    
Maximum | Cash-settled SARs      
Accounting Policies [Line Items]      
Expiration period 7 years    
Other Property and Equipment      
Accounting Policies [Line Items]      
Depreciation $ 700,000 $ 1,100,000 $ 900,000
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