Earnings Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Net Income Attributable to Southwestern Energy (in thousands)	$ 175,173	$ 160,741	$ 479,236	$ 454,607
Number of common shares, Weighted average outstanding	347,239,793	345,587,569	347,070,330	345,326,985
Number of common shares, Weighted average and potential dilutive outstanding	349,998,789	349,228,576	349,891,885	349,308,957
Net Income Attributable to Southwestern Energy stockholders - Basic	$ 0.50	$ 0.47	$ 1.38	$ 1.32
Net income attributable to Southwestern Energy stockholders - Diluted	$ 0.50	$ 0.46	$ 1.37	$ 1.30
Stock Options [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options	2,490,783	3,438,923	2,591,687	3,747,293
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	783,823	907,284	811,552	510,067
Restricted Stock [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options	268,213	202,084	229,868	234,679
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,645	59,153	7,114	12,627