Basis of Presentation and New Accounting Standards (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current assets inventory, underground storage	$ 7,800,000	$ 10,000,000
Current assets inventory, tubulars & other equipment	38,400,000	25,100,000
Other assets non-current inventory, gathering systems pipe	19,500,000	20,600,000
Natural gas storage revenue	900,000	2,500,000	3,400,000
Outstanding checks included in accounts payable	47,700,000	23,100,000
Cash flow hedges impact on ceiling value	262,500,000
Ceiling test impairment, amount net of tax			558,300,000
Interest Paid, Net	19,159,000	24,049,000	16,453,000
Income Taxes Paid, Net	4,198,000	14,368,000	(41,469,000)
Capital Expenditures Incurred but Not yet Paid	30,389,000	46,588,000	28,951,000
Average exercise price of outstanding options	$ 11.78	$ 9.42	$ 8.33
Treasury stock, shares	98,889	156,636
Overproduction [Member]
Gas imbalance volume amount in Bcf	6.1	3.9
Gas imbalance asset (liability)	22,500,000	13,300,000
Underproduction [Member]
Gas imbalance volume amount in Bcf	6.4	3.7
Gas imbalance asset (liability)	22,900,000	12,800,000
Henry Hub Natural Gas [Member]
Full cost ceiling test, price per MMBtu	4.12	4.38	3.87
West Texas Intermediate Oil [Member]
Full cost ceiling test, price per barrel	$ 92.71	$ 75.96	$ 57.65
Stock Options [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options	3,577,104	4,753,530
Antidilutive securities excluded from computation of earnings per share, shares	881,254	548,160	6,683,085
Restricted Stock [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options	241,044	700,512
Antidilutive securities excluded from computation of earnings per share, shares	135,352	39,600	836,861