Derivative Financial Instruments (Narrative) (Details) (USD $)	1 Months Ended		12 Months Ended					3 Months Ended	2 Months Ended	12 Months Ended
	Jan. 31, 2012	Jul. 31, 2011	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2011 2012 Diesel Swaps [Member] bbl	Dec. 31, 2011 NGL Swaps [Member] bbl	Dec. 31, 2011 NGL Collar Contracts with Short Puts [Member] bbl	May 31, 2012 2012 Roll Adjustment Swap [Member] bbl	Feb. 24, 2012 2013 Roll Adjustment Swap [Member] bbl	Dec. 31, 2013 2013 Roll Adjustment Swap [Member] bbl	Dec. 31, 2011 Ceiling [Member] NGL Collar Contracts with Short Puts [Member]	Dec. 31, 2011 Floor [Member] NGL Collar Contracts with Short Puts [Member]	Dec. 31, 2011 Short Put [Member] NGL Collar Contracts with Short Puts [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Swap contract notional volume Bbls per day					500	750	3,000	3,000	3,000	3,000
Average fixed price per Bbl					119.49	$ 35.03		$ 0.28	$ 0.43	$ 0.43	$ 79.99	$ 67.70	$ 55.76
Terminated diesel swap derivatives cash proceeds	$ 1,800,000
Proceeds from termination of interest rate derivatives		26,100,000
Net deferred gains from hedging in AOCI			(3,130,000)	7,361,000
Net deferred losses on the effective portions of discontinued commodity hedges			3,100,000
Net deferred losses on the effective portions of discontinued interest rate hedges			1,700,000
Net deferred gains or losses associated to net deferred tax provisions			1,700,000
Expected to reclassify accumulated other comprehensive income - Hedging net deferred gains			3,100,000
Cash flow hedge loss reclassified to interest expense			317,000
Expected to reclassify net deferred income tax provision			1,300,000
Derivative fixed interest rate		3.06%	3.06%
Derivative fixed interest rate term, years			10
Notional amount of debt		$ 200,000,000	$ 200,000,000	$ 189,000,000