Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Natural Gas Properties (Unaudited) (Standardized Measure of Discounted Future Cash Flows Relating to Proved Reserves Disclosure) (Details)

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Supplemental Information on Oil and Natural Gas Properties (Unaudited) (Standardized Measure of Discounted Future Cash Flows Relating to Proved Reserves Disclosure) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Net Cash Flows [Abstract]            
Future cash inflows       $ 20,891,469 $ 11,794,080 $ 5,920,328
Future costs            
Production       (6,717,088) (2,923,959) (1,692,871)
Development and net abandonment       (3,058,861) (1,429,787) (680,948)
Future net inflows before income taxes       11,115,520 7,440,334 3,546,509
Future income taxes       (941,768) (782,470) (166,985)
Future net cash flows       10,173,752 6,657,864 3,379,524
10% discount factor       (5,222,726) (3,716,571) (1,822,842)
Standardized measure of discounted future net cash flows $ 2,941,293 $ 1,556,682 $ 1,556,682 $ 4,951,026 $ 2,941,293 $ 1,556,682
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Roll Forward]            
Standardized measure at the beginning of the period 2,941,293 1,556,682 809,832      
Sales and transfers, net of production costs (579,744) (481,306) (294,172)      
Net change in sales and transfer prices, net of production costs (387,970) 222,802 176,234      
Net change due to purchases of in place reserves 2,975,296 554,697 129,454      
Net change due to sales of in place reserves (303,526) 0 0      
Extensions, discoveries, and improved recovery, net of future production and development costs incurred 607,146 1,001,873 635,000      
Changes in future development cost 205,398 40,483 (8,148)      
Previously estimated development costs incurred 134,037 91,900 45,131      
Revisions of quantity estimates (420,488) (167,096) (79,325)      
Accretion of discount 314,921 157,676 80,983      
Net change in income taxes (210,641) (187,841) (20,073)      
Changes in production rates, timing and other (324,696) 151,423 81,766      
Aggregate change 2,009,733 1,384,611 746,850      
Standardized measure at the end of period $ 4,951,026 $ 2,941,293 $ 1,556,682