Fair Value Measurements (Fair Value Hierarchy) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Oil derivative contracts-current asset	$ 0	$ 142,846
Total Assets		142,846
Oil derivative contracts-current liability	69,279	0
Total Liabilities	69,279
Quoted Prices in Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Oil derivative contracts-current asset		0
Total Assets		0
Oil derivative contracts-current liability	0
Total Liabilities	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Oil derivative contracts-current asset		90,012
Total Assets		90,012
Oil derivative contracts-current liability	68,753
Total Liabilities	68,753
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Oil derivative contracts-current asset		52,834
Total Assets		$ 52,834
Oil derivative contracts-current liability	526
Total Liabilities	$ 526