Quarterly Results (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quarterly Results (Unaudited)
Revenues from external customers	$ 744,150	$ 767,255	$ 765,166	$ 676,335	$ 670,431	$ 682,172	$ 589,943	$ 668,117	$ 2,952,906	$ 2,610,663	$ 2,145,779
Operating income	263,890	295,718	282,542	232,651	256,685	270,136	206,317	288,090	1,074,801	1,021,228	(34,966)
Net income	158,533	175,173	167,454	136,609	149,418	160,638	122,009	171,768	637,769	603,833	(35,792)
Net Income (Loss) Attributable to Southwestern Energy	158,533	175,173	167,454	136,609	149,511	160,741	122,069	171,797	637,769	604,118	(35,650)
Earnings per share attributable to Southwestern Energy stockholders - Basic	$ 0.47	$ 0.50	$ 0.48	$ 0.39	$ 0.43	$ 0.47	$ 0.35	$ 0.50	$ 1.84	$ 1.75	$ (0.10)
Earnings per share attributable to Southwestern Energy stockholders - Diluted	$ 0.45	$ 0.50	$ 0.48	$ 0.39	$ 0.43	$ 0.46	$ 0.35	$ 0.49	$ 1.82	$ 1.73	$ (0.10)
Impairment of natural gas and oil properties									$ 0	$ 0	$ 907,812