Earnings Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Net Income Attributable to Southwestern Energy (in thousands)	$ 167,454	$ 122,069	$ 304,063	$ 293,866
Number of common shares, Weighted average outstanding	347,132,830	345,288,773	346,984,194	345,194,534
Number of common shares, Weighted average and potential dilutive outstanding	349,970,819	349,341,731	349,840,044	349,364,654
Net Income Attributable to Southwestern Energy stockholders - Basic	$ 0.48	$ 0.35	$ 0.88	$ 0.85
Net income attributable to Southwestern Energy stockholders - Diluted	$ 0.48	$ 0.35	$ 0.87	$ 0.84
Stock Options [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options and effect of issuance of nonvested restricted common stock	2,583,711	3,812,833	2,643,537	3,911,348
Antidilutive securities excluded from computation of earnings per share, shares	749,910	500,774	813,878	463,142
Restricted Stock [Member]
Number of common shares, issued upon assumed exercise of outstanding stock options and effect of issuance of nonvested restricted common stock	254,278	240,125	212,313	258,772
Antidilutive securities excluded from computation of earnings per share, shares	3,421	6,543	3,041	8,781