Condensed Consolidating Financial Information (Condensed Consolidating Statement of Operations) (Details) (USD $) In Thousands, 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
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
Gas purchases									709,091		611,161		482,836
Operating expenses									240,944		191,771		136,541
General and administrative expenses									158,041		145,563		122,618
Depreciation, depletion and amortization									704,511		590,332		493,658
Impairment of natural gas and oil properties									0		0		907,812
Taxes, other than income taxes									65,518		50,608		37,280
Total operating costs and expenses									1,878,105		1,589,435		2,180,745
Operating Income (Loss)	263,890	295,718	282,542	232,651	256,685	270,136	206,317	288,090	1,074,801		1,021,228		(34,966)
Other income, net									264		427		1,449
Equity in earnings of subsidiaries									0		0		0
Interest expense									24,075	[1]	26,163	[1]	18,638	[1]
Income (Loss) Before Income Taxes									1,050,990		995,492		(52,155)
Provision for income taxes									413,221	[1]	391,659	[1]	(16,363)
Net Income (Loss)	158,533	175,173	167,454	136,609	149,418	160,638	122,009	171,768	637,769		603,833		(35,792)
Less: Net Loss Attributable to Noncontrolling Interest									0		(285)		(142)
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)
Parent [Member]
Revenues from external customers									0		0		0
Gas purchases									0		0		0
Operating expenses									0		0		0
General and administrative expenses									0		0		0
Depreciation, depletion and amortization									0		0		0
Impairment of natural gas and oil properties													0
Taxes, other than income taxes									0		0		0
Total operating costs and expenses									0		0		0
Operating Income (Loss)									0		0		0
Other income, net									0		0		0
Equity in earnings of subsidiaries									637,769		604,118		(35,650)
Interest expense									0		0		0
Income (Loss) Before Income Taxes									637,769		604,118		(35,650)
Provision for income taxes									0		0		0
Net Income (Loss)									637,769		604,118		(35,650)
Less: Net Loss Attributable to Noncontrolling Interest											0		0
Net income (loss) attributable to Southwestern Energy											604,118		(35,650)
Guarantors [Member]
Revenues from external customers									2,803,385		2,488,105		2,071,746
Gas purchases									710,487		612,745		483,922
Operating expenses									380,154		293,713		201,964
General and administrative expenses									141,499		127,022		109,870
Depreciation, depletion and amortization									665,615		559,845		472,757
Impairment of natural gas and oil properties													907,812
Taxes, other than income taxes									53,950		44,200		33,935
Total operating costs and expenses									1,951,705		1,637,525		2,210,260
Operating Income (Loss)									851,680		850,580		(138,514)
Other income, net									306		242		1,388
Equity in earnings of subsidiaries									0		0		0
Interest expense									11,277		10,777		12,760
Income (Loss) Before Income Taxes									840,709		840,045		(149,886)
Provision for income taxes									332,795		330,879		(53,549)
Net Income (Loss)									507,914		509,166		(96,337)
Less: Net Loss Attributable to Noncontrolling Interest											(285)		(142)
Net income (loss) attributable to Southwestern Energy											509,451		(96,195)
Non-Guarantors [Member]
Revenues from external customers									411,998		318,232		207,672
Gas purchases									0		0		0
Operating expenses									118,713		91,164		66,682
General and administrative expenses									19,700		19,525		13,196
Depreciation, depletion and amortization									38,896		30,487		20,901
Impairment of natural gas and oil properties													0
Taxes, other than income taxes									11,568		6,408		3,345
Total operating costs and expenses									188,877		147,584		104,124
Operating Income (Loss)									223,121		170,648		103,548
Other income, net									(42)		185		61
Equity in earnings of subsidiaries									0		0		0
Interest expense									12,798		15,386		5,878
Income (Loss) Before Income Taxes									210,281		155,447		97,731
Provision for income taxes									80,426		60,780		37,186
Net Income (Loss)									129,855		94,667		60,545
Less: Net Loss Attributable to Noncontrolling Interest											0		0
Net income (loss) attributable to Southwestern Energy											94,667		60,545
Eliminations [Member]
Revenues from external customers									(262,477)		(195,674)		(133,639)
Gas purchases									(1,396)		(1,584)		(1,086)
Operating expenses									(257,923)		(193,106)		(132,105)
General and administrative expenses									(3,158)		(984)		(448)
Depreciation, depletion and amortization									0		0		0
Impairment of natural gas and oil properties													0
Taxes, other than income taxes									0		0		0
Total operating costs and expenses									(262,477)		(195,674)		(133,639)
Operating Income (Loss)									0		0		0
Other income, net									0		0		0
Equity in earnings of subsidiaries									(637,769)		(604,118)		35,650
Interest expense									0		0		0
Income (Loss) Before Income Taxes									(637,769)		(604,118)		35,650
Provision for income taxes									0		0		0
Net Income (Loss)									(637,769)		(604,118)		35,650
Less: Net Loss Attributable to Noncontrolling Interest											0		0
Net income (loss) attributable to Southwestern Energy											$ (604,118)		$ 35,650

[1] (1) Interest income, interest expense and the provision (benefit) for income taxes by segment are an allocation of corporate amounts as cash equivalents, debt and income tax expense allocated as they are incurred at the corporate level.