Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Capitalized Costs Related to Oil and Gas Producing Activities (Details)

v3.6.0.2
Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Capitalized Costs Related to Oil and Gas Producing Activities (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Reserve Quantities [Line Items]    
Proven properties $ 4,491,615 $ 3,606,641
Unproven properties 1,580,305 1,817,701
Capitalized costs, gross 6,071,920 5,424,342
Accumulated depreciation, depletion, amortization and impairment reserve (3,778,043) (2,820,113)
Net capitalized costs 2,293,877 2,604,229
Investment in Grizzly Oil Sands ULC    
Reserve Quantities [Line Items]    
Proven properties 70,266 81,473
Unproven properties 80,892 82,388
Capitalized costs, gross 151,158 163,861
Accumulated depreciation, depletion, amortization and impairment reserve (1,578) (1,531)
Net capitalized costs $ 149,580 $ 162,330