Annual report pursuant to Section 13 and 15(d)

Income Taxes (Narrative) (Details)

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Income Taxes (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Business Acquisition [Line Items]      
Operating loss carryforwards $ 527,200    
Deferred income tax valuation allowance 180,777 $ 170,302  
Non-deductible merger expenses 5,537 0 $ 0
Statutory depletion carryforward 5,381 $ 0 $ 0
Statutory depletion carryforward 24,900    
Operating loss carryforwards, subject to expiration 496,500    
Post 2017, net operating loss 30,700    
Carrizo      
Business Acquisition [Line Items]      
Operating loss carryforwards 288,200    
Deferred income tax valuation allowance $ 159,300