Supplemental Disclosures About Oil And Gas Producing Activities (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Capitalized interest	$ 24,848,000	$ 23,369,000	$ 20,746,000
Interest costs capitalized	$ 11,800,000	$ 9,600,000	$ 5,300,000
Reserves discount factor	10.00%
Crude Oil And Condensate, Per Barrel [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Average market prices used in reserves estimates	102.03	95.28	74.39
Natural Gas Liquids [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Average market prices used in reserves estimates	32.12	44.90	35.18
Natural Gas, Per Thousand Cubic Feet [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Average market prices used in reserves estimates	2.08	3.24	3.50