Derivative Instruments and Hedging Activities (Derivatives Fair Value By Balance Sheet Location) (Details) (Not Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Asset, Fair Value, Net	$ 1,511	$ 1,924
Derivative Liability, Fair Value, Net	(868)	(241)
Derivative, Fair Value, Net	643	1,683
Current Liabilities - Fair Market Value of Derivatives [Member] | Natural gas [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Gross Liability	(537)	(125)
Derivative Assets (Liability), Fair Value, Gross Liability Net	537	125
Current assets - Fair market value of derivatives [Member] | Crude oil [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,511	1,674
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Assets (Liability), Fair Value, Gross Asset Net	1,511	1,674
Noncurrent Assets - Other Long-Term Assets [Member] | Crude oil [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	250
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Assets (Liability), Fair Value, Gross Asset Net	0	250
Non-current liabilities - Other long-term liabilities [Member] | Natural gas [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Gross Liability	(92)	(116)
Derivative Assets (Liability), Fair Value, Gross Liability Net	92	116
Non-current liabilities - Other long-term liabilities [Member] | Crude oil [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Gross Liability	(239)	0
Derivative Assets (Liability), Fair Value, Gross Liability Net	$ 239	$ 0