Fair Value Measurements (Fair Value Hierarchy Table) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current asset	$ 4,699	$ 142,846
Oil derivative contracts - long-term asset	31	0
Total Assets	4,730	142,846
Oil derivative contracts - current liability	107,105	0
Oil derivative contracts - long-term liability	67	0
Total Liabilities	107,172
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	0
Oil derivative contracts - long-term asset	0
Total Assets	0	0
Oil derivative contracts - current liability	0
Oil derivative contracts - long-term liability	0
Total Liabilities	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	2,619	90,012
Oil derivative contracts - long-term asset	31
Total Assets	2,650	90,012
Oil derivative contracts - current liability	105,310
Oil derivative contracts - long-term liability	22
Total Liabilities	105,332
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Oil derivative contracts - current asset	2,080	52,834
Oil derivative contracts - long-term asset	0
Total Assets	2,080	$ 52,834
Oil derivative contracts - current liability	1,795
Oil derivative contracts - long-term liability	45
Total Liabilities	$ 1,840