Annual report pursuant to Section 13 and 15(d)

Income Taxes - Narrative (Details)

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Income Taxes - Narrative (Details) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Operating Loss Carryforwards [Line Items]      
Valuation allowance increase (decrease) $ (86,800,000) $ (347,000,000) $ 342,600,000
Valuation allowance of deferred tax assets 211,987,000 298,830,000 645,841,000
Impairment of oil and natural gas properties 0 $ 0 $ 715,495,000
Federal      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforward 782,700,000    
State      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforward 205,700,000    
Foreign Tax Authority      
Operating Loss Carryforwards [Line Items]      
Tax credit carryforward $ 1,800,000