Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net income	$ 107,704	$ 136,609
Number of common shares, Weighted average outstanding	348,000,074	346,833,906
Number of common shares, Weighted average and potential dilutive outstanding	349,990,725	349,697,327
Net income attributable to Southwestern Energy stockholders - Basic	$ 0.31	$ 0.39
Net income attributable to Southwestern Energy stockholders - Diluted	$ 0.31	$ 0.39
Stock Options [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options	1,889,691	2,700,902
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,702,166	843,324
Restricted Stock [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options	100,960	162,519
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	657,763	4,928