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 ($)
Mcf / bbl
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Summary Of Significant Accounting Policies [Line Items]      
Accounts receivable, collection period 30 days    
Allowance for doubtful accounts $ 0 $ 0  
Conversion ratio, gas to barrels of oil (in Mcf of gas) | Mcf / bbl 6    
Capitalized costs of oil and natural gas properties excluded from amortization $ 2,873,037,000 2,912,974,000  
Unrecognized tax benefits 0    
Gas imbalance receivable   0  
Cash and cash equivalents 52,297,000 99,557,000  
Net cash used in investing activities (643,091,000) (2,474,168,000) $ (720,582,000)
Investment in Grizzly Oil Sands ULC      
Summary Of Significant Accounting Policies [Line Items]      
Equity method investment recognized impairment charges $ 0 0 23,100,000
Minimum      
Summary Of Significant Accounting Policies [Line Items]      
Useful life 3 years    
Minimum | Restricted stock      
Summary Of Significant Accounting Policies [Line Items]      
Vesting period 1 year    
Maximum      
Summary Of Significant Accounting Policies [Line Items]      
Useful life 30 years    
Maximum | Restricted stock      
Summary Of Significant Accounting Policies [Line Items]      
Vesting period 4 years    
Accounting Standards Update 2016-02      
Summary Of Significant Accounting Policies [Line Items]      
Lease liability $ 110,000,000    
Accounting Standards Update 2016-18      
Summary Of Significant Accounting Policies [Line Items]      
Cash and cash equivalents $ 0   185,000,000
Net cash used in investing activities   $ 185,000,000 $ (185,000,000)