Derivative Instruments and Hedging Activities (Derivatives Designated as Hedging Instruments/ Derivatives Not Designated as Hedging Instruments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended		15 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss), net	$ (1,598)	$ 1,977	$ 0	$ 0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income (ineffective portion and amount excluded from effectiveness testing)	(282)	40	177	159
Amount of gain (loss) reclassified from OCI into income (effective portion)	260	772	(361)	88
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss), net	(1,598)	1,977	0	0
Commodity Contract [Member] | Natural gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss), net	0	0	0	0
Total gain (loss), net	(205)	(536)	0	0
Unrealized gain (loss), net	(205)	(536)	0	0
Commodity Contract [Member] | Crude Oil [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss), net	0	0	0	0
Total gain (loss), net	(1,393)	2,513	0	0
Unrealized gain (loss), net	$ (1,393)	$ 2,513	$ 0	$ 0