Fair Value Measurements (Fair Value Heirarchy Table) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets, Fair Value Disclosure [Abstract]
Oil derivative contracts	$ 28,627	$ 19,513
Liabilities, Fair Value Disclosure [Abstract]
Oil derivative contracts	(1,982)	(26,440)
Total	26,645	(6,927)
Quoted Prices in Active Markets (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
Oil derivative contracts	0	0
Liabilities, Fair Value Disclosure [Abstract]
Oil derivative contracts	0	0
Total	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
Oil derivative contracts	25,444	19,513
Liabilities, Fair Value Disclosure [Abstract]
Oil derivative contracts	(1,895)	(26,440)
Total	23,549	(6,927)
Significant Unobservable Inputs (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
Oil derivative contracts	3,183	0
Liabilities, Fair Value Disclosure [Abstract]
Oil derivative contracts	(87)	0
Total	$ 3,096	$ 0