Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 592,527	$ 600,558
(Loss) gain on crude contracts	(214,385)	400,672
Gain on sale of assets and other income	1,843	2,498
Total revenues and other income	379,985	1,003,728
Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	490,796	528,069
Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	21,569	12,563
Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	80,162	59,926
United States \| Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	114,490	131,236
United States \| Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	7,528	5,503
United States \| Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6,443	5,558
United States Offshore \| Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	328,341	346,972
United States Offshore \| Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	10,054	5,026
United States Offshore \| Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	22,138	14,995
Canada \| Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	29,903	23,383
Canada \| Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3,987	2,034
Canada \| Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	51,581	39,373
Canada Offshore \| Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	18,062	24,614
Other \| Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 0	$ 1,864

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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