Organization and Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended			24 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012
Asset Retirement Obligation, Period Increase (Decrease)		$ 39,000,000
Gains related to the sale of natural gas in underground storage	1,000,000			(900,000)
Outstanding checks included in accounts payable	4,900,000	12,100,000		12,100,000
Current assets inventory, tubulars & other equipment	3,700,000
Other Inventory, Noncurrent	16,000,000
Natural gas and oil reserves discount	10.00%
Cash flow hedges impact on ceiling value	70,700,000
Amount recognized is the largest amount of tax benefit, threshold	50.00%
Net capitalized costs exceeding ceiling		1,192,400,000
Cash paid during the year for interest, net of amounts capitalized	36,267,000	17,311,000	19,159,000
Cash paid during the year for income taxes	18,787,000	818,000	4,198,000
Increase (decrease) in noncash property additions	(12,730,000)	(26,240,000)	30,389,000
Common Stock in Treasury, Shares	9,924,000	64,715,000		64,715,000
NGL [Member]
Full cost ceiling test, Price	43.45
Over Production [Member]
Gas imbalance volume amount in Bcf	11.2	8.4		8.4
Gas imbalance asset (liability)	37,900,000	28,400,000		28,400,000
Under Production [Member]
Gas imbalance volume amount in Bcf	12.5	9.4		9.4
Gas imbalance asset (liability)	(38,500,000)	(29,900,000)		(29,900,000)
Henry Hub Natural Gas [Member]
Full cost ceiling test, Price	3.67	2.76	4.12
West Texas Intermediate Oil [Member]
Full cost ceiling test, Price	93.42	91.21	92.71
Stock Options [Member]
Number of common shares, Issued upon assumed exercise of outstanding stock options	1,569,665		3,577,104
Outstanding options average exercise price	$ 28.03		$ 11.78
Antidilutive securities excluded from computation of earnings per share, shares	1,634,695	1,716,109	881,254
Restricted Stock [Member]
Number of common shares, Issued upon assumed exercise of outstanding stock options	258,396		241,044
Antidilutive securities excluded from computation of earnings per share, shares	114,433	602,429	135,352
Exploration and Production [Member]
Energy Related Inventory, Gas Stored Underground	3,700,000	5,600,000		5,600,000
Current assets inventory, tubulars & other equipment	34,100,000	22,500,000		22,500,000
Midstream Services [Member]
Other Inventory, Noncurrent	$ 15,100,000	$ 13,800,000		$ 13,800,000
Gathering Systems [Member]
Straight-line depreciation period	25 years