Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Narrative (Details)

v3.8.0.1
Summary of Significant Accounting Policies - Narrative (Details)
 12 Months Ended
Dec. 31, 2017
USD ($)
Mcf / bbl
purchaser
Dec. 31, 2016
USD ($)
Dec. 31, 2015
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 | Mcf / bbl 6    
Capitalized costs of oil and natural gas properties excluded from amortization $ 2,912,974,000 1,580,305,000  
Gas imbalance receivable 200,000 200,000  
Investment in Grizzly Oil Sands ULC      
Summary Of Significant Accounting Policies [Line Items]      
Equity method investment recognized impairment charges $ 0 $ 23,100,000 $ 101,600,000
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    
Customer concentration risk | Accounts receivable      
Summary Of Significant Accounting Policies [Line Items]      
Concentration risk, number of purchasers | purchaser 3