Fair Value Measurements (Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Oil derivative contracts - current assets	$ 11,936	$ 93,080
Oil derivative contract - long-term assets	0	4,195
Total Assets	11,936	97,275
Oil derivative contracts - current liabilities	(8,346)	0
Total Liabilities	(8,346)
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Oil derivative contracts - current assets	0	0
Oil derivative contract - long-term assets		0
Total Assets	0	0
Oil derivative contracts - current liabilities	0
Total Liabilities	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Oil derivative contracts - current assets	8,503	81,621
Oil derivative contract - long-term assets		2,030
Total Assets	8,503	83,651
Oil derivative contracts - current liabilities	(6,522)
Total Liabilities	(6,522)
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Oil derivative contracts - current assets	3,433	11,459
Oil derivative contract - long-term assets		2,165
Total Assets	3,433	$ 13,624
Oil derivative contracts - current liabilities	(1,824)
Total Liabilities	$ (1,824)

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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