Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) (Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves) (Details)

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Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) (Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items]      
Sales and transfers of oil and gas produced, net of production costs $ (486,185) $ (530,098) $ (197,559)
Net changes in prices, production costs, and development costs (1,412,181) 97,716 65,573
Acquisition of oil and gas reserves in place 83,340 14,266 0
Extensions and discoveries 262,895 790,533 130,826
Previously estimated development costs incurred during the period 117,540 68,227 43,478
Revisions of previous quantity estimates, less related production costs (98,162) (37,801) (3,591)
Accretion of discount 142,717 57,847 34,864
Net changes in income taxes 412,240 (295,226) (30,239)
Change in production rates and other 314,960 683,237 186,473
Total change in standardized measure of discounted future net cash flows (662,836) 848,701 229,825
Diamondback Energy, Inc      
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items]      
Sales and transfers of oil and gas produced, net of production costs 0 0 (12,524)
Change in ownership interest in Diamondback 0 0 (52,145)
Net changes in prices, production costs, and development costs 0 0 3,312
Acquisition of oil and gas reserves in place 0 0 21,968
Extensions and discoveries 0 0 39,776
Previously estimated development costs incurred during the period 0 0 5,517
Revisions of previous quantity estimates, less related production costs 0 0 (9,143)
Accretion of discount 0 0 4,175
Net changes in income taxes 0 0 (12,137)
Change in production rates and other 0 0 2,862
Total change in standardized measure of discounted future net cash flows 0 0 (8,339)
Investment in Grizzly Oil Sands ULC      
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items]      
Sales and transfers of oil and gas produced, net of production costs 114 4,664 0
Net changes in prices, production costs, and development costs 0 (76,518) 0
Acquisition of oil and gas reserves in place 0 0 0
Extensions and discoveries 0 7,107 0
Previously estimated development costs incurred during the period 47 0 0
Revisions of previous quantity estimates, less related production costs (103,282) 10,659 0
Accretion of discount 9,375 14,946 0
Net changes in income taxes 0 9,162 0
Change in production rates and other 0 (25,738) 0
Total change in standardized measure of discounted future net cash flows $ (93,746) $ (55,718) $ 0