Derivative Financial Instruments (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended
	Apr. 30, 2012 Y	Mar. 31, 2012 Y	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net deferred losses from hedging in AOCI		$ (1,550,000)	$ (3,130,000)
Net deferred losses on the effective portions of discontinued commodity hedges		2,300,000
Net deferred gains or losses associated to net deferred tax benefits		797,000
Expected to reclassify accumulated other comprehensive income - Hedging net deferred gains		2,300,000
Expected to reclassify net deferred income tax provisions		797,000,000
Derivative fixed interest rate	3.21%	3.06%
Derivative fixed interest rate term, years	10	10
Notional amount of debt	$ 250,000,000	$ 200,000,000
NGL Swap [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Swap contract notional volume Bbls per day		750
Average fixed price per Bbl		35.03
NGL Collar Contracts With Short Put [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Swap contract notional volume Bbls per day		3,000
Ceiling [Member] | NGL Collar Contracts With Short Put [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Average fixed price per Bbl		79.99
Floor [Member] | NGL Collar Contracts With Short Put [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Average fixed price per Bbl		67.70
Short Put [Member] | NGL Collar Contracts With Short Put [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Average fixed price per Bbl		55.76