Derivative Instruments and Hedging Activities (Derivatives Fair Value By Balance Sheet Location) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Derivative Asset, Fair Value, Net	$ 6,627	$ 2,499
Derivative Liability, Fair Value, Net	(350)	0
Derivative, Fair Value, Net	6,277	2,499
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Net	2,702	2,499
Derivative Liability, Fair Value, Net	0	0
Derivative, Fair Value, Net	2,702	2,499
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Net	3,925	0
Derivative Liability, Fair Value, Net	(350)	0
Derivative, Fair Value, Net	3,575	0
Current assets - Fair market value of derivatives [Member] | Designated as Hedging Instrument [Member] | Natural gas [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Assets (Liability), Fair Value, Gross Asset Net	0	0
Current assets - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Natural gas [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	19	0
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Assets (Liability), Fair Value, Gross Asset Net	19	0
Non-current assets - Other long-term assets [Member] | Designated as Hedging Instrument [Member] | Natural gas [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Assets (Liability), Fair Value, Gross Asset Net	0	0
Non-current assets - Other long-term assets [Member] | Not Designated as Hedging Instrument [Member] | Crude oil [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,982	0
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Assets (Liability), Fair Value, Gross Asset Net	1,982	0
Current liabilities - Fair market value of derivatives [Member] | Designated as Hedging Instrument [Member] | Crude oil [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	2,702	2,499
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative Assets (Liability), Fair Value, Gross Liability Net	2,702	2,499
Current liabilities - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Crude oil [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	1,924	0
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative Assets (Liability), Fair Value, Gross Liability Net	1,924	0
Non-current liabilities - Other long-term liabilities [Member] | Designated as Hedging Instrument [Member] | Crude oil [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Derivative Assets (Liability), Fair Value, Gross Liability Net	0	0
Non-current liabilities - Other long-term liabilities [Member] | Not Designated as Hedging Instrument [Member] | Natural gas [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Liability, Fair Value, Gross Liability	(350)	0
Derivative Assets (Liability), Fair Value, Gross Liability Net	$ (350)	$ 0