Derivative Instruments and Hedging Activities (Gain or loss on derivative contracts) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) on fair value adjustments			$ 5,728	$ (2,929)
Total gain (loss) on derivative instruments	9,944	(3,686)	2,746	(2,123)
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) on settlements	35	(16)	(144)	(123)
Net gain (loss) on fair value adjustments	55	81	(77)	178
Total gain (loss) on derivative instruments	90	65	(221)	55
Crude Oil [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) on settlements	(497)	(618)	(2,838)	804
Net gain (loss) on fair value adjustments	10,351	(3,133)	5,805	(2,982)
Total gain (loss) on derivative instruments	$ 9,854	$ (3,751)	$ 2,967	$ (2,178)