Fair Value Measurements (Fair Value Hierarchy Table) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current assets	$ 236	$ 187
Oil derivative contracts - long-term assets	3,021	0
Total Assets	3,257	187
Oil derivative contracts - current liabilities	(129,124)	(53,865)
Oil derivative contracts - long-term liabilities	(10,188)	(5,087)
Total Liabilities	(139,312)	(58,952)
Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current assets	0	0
Oil derivative contracts - long-term assets	0
Total Assets	0	0
Oil derivative contracts - current liabilities	0	0
Oil derivative contracts - long-term liabilities	0	0
Total Liabilities	0	0
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current assets	236	187
Oil derivative contracts - long-term assets	3,021
Total Assets	3,257	187
Oil derivative contracts - current liabilities	(129,124)	(53,865)
Oil derivative contracts - long-term liabilities	(10,188)	(5,087)
Total Liabilities	(139,312)	(58,952)
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current assets	0	0
Oil derivative contracts - long-term assets	0
Total Assets	0	0
Oil derivative contracts - current liabilities	0	0
Oil derivative contracts - long-term liabilities	0	0
Total Liabilities	$ 0	$ 0

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