Fair Value Measurements (Fair Value Hierarchy Table) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current asset	$ 3,572	$ 0
Oil derivative contracts - long-term	1,237	0
Total Assets	4,809
Oil derivative contracts - long-term liabilities	(407)	0
Oil derivative contracts - current liability	0	(69,279)
Total Liabilities	(407)	(69,279)
Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current asset	0
Oil derivative contracts - long-term	0
Total Assets	0
Oil derivative contracts - long-term liabilities	0
Oil derivative contracts - current liability		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 asset	3,473
Oil derivative contracts - long-term	1,237
Total Assets	4,710
Oil derivative contracts - long-term liabilities	(407)
Oil derivative contracts - current liability		(68,753)
Total Liabilities	(407)	(68,753)
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current asset	99
Oil derivative contracts - long-term	0
Total Assets	99
Oil derivative contracts - long-term liabilities	0
Oil derivative contracts - current liability		(526)
Total Liabilities	$ 0	$ (526)