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)

v3.10.0.1
Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Results of Operations for Producing Activities (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
usd_per_mcf
Dec. 31, 2017
USD ($)
usd_per_mcf
Dec. 31, 2016
USD ($)
usd_per_mcf
Results of Operations for Oil and Gas Producing Activities [Line Items]      
Revenues $ 1,355,044,000 $ 1,320,303,000 $ 385,910,000
Production costs (415,308,000) (350,367,000) (248,125,000)
Depletion (476,517,000) (358,792,000) (243,098,000)
Impairment 0 0 (715,495,000)
Results of operations, before income taxes 463,219,000 611,144,000 (820,808,000)
Income Tax Expense (Benefit), Continuing Operations [Abstract]      
Current 254,000 3,362,000 0
Deferred (322,000) (3,602,000) 0
Income tax expense (68,000) (240,000) 0
Results of operations from producing activities $ 463,287,000 $ 611,384,000 $ (820,808,000)
Depletion per Mcf of gas equivalent (usd per Mcfe) | usd_per_mcf 0.96 0.90 0.92
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 (13,000)
Depletion 0 0 0
Results of operations, before income taxes 0 0 (13,000)
Income Tax Expense (Benefit), Continuing Operations [Abstract]      
Income tax expense 0 0 0
Results of operations from producing activities $ 0 $ 0 $ (13,000)