Fair Value Measurements (Fair Value Hierarchy Table) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current assets	$ 55,615	$ 93,080
Oil derivative contracts - long-term assets	11,483	4,195
Total Assets	67,098	97,275
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	0
Total Assets	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	46,099	81,621
Oil derivative contracts - long-term assets	9,799	2,030
Total Assets	55,898	83,651
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current assets	9,516	11,459
Oil derivative contracts - long-term assets	1,684	2,165
Total Assets	$ 11,200	$ 13,624