Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Results of Operations for Producing Activities (Details)

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Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Results of Operations for Producing Activities (Details)
12 Months Ended
Dec. 31, 2019
USD ($)
usd_per_mcf
Dec. 31, 2018
USD ($)
usd_per_mcf
Dec. 31, 2017
USD ($)
usd_per_mcf
Results of Operations for Oil and Gas Producing Activities [Line Items]      
Revenues $ 1,137,648,000 $ 1,478,523,000 $ 1,106,624,000
Production costs (403,294,000) (415,308,000) (350,367,000)
Depletion (539,379,000) (476,517,000) (358,792,000)
Impairment (2,039,770,000) 0 0
Income tax expense (benefit) 7,563,000 68,000 240,000
Results of operations from producing activities $ (1,837,232,000) $ 586,766,000 $ 397,705,000
Depletion per Mcf of gas equivalent (usd per Mcfe) | usd_per_mcf 1.08 0.96 0.90
Investment in Grizzly Oil Sands ULC      
Results of Operations for Oil and Gas Producing Activities [Line Items]      
Revenues $ 0 $ 0 $ 0
Production costs 0 0 0
Depletion 0 0 0
Income tax expense (benefit) 0 0 0
Results of operations from producing activities $ 0 $ 0 $ 0