Derivatives and Risk Management (Cash Flow Hedges on Volumes of Natural Gas Production) (Details)	Mar. 31, 2013 ft3
Year 2013 [Member]
Derivative [Line Items]
Volume of Natural Gas Production (in Bcf), Cash Flow Hedges	139,600,000,000
Year 2014 [Member]
Derivative [Line Items]
Volume of Natural Gas Production (in Bcf), Cash Flow Hedges	18,300,000,000

Volume (in Bcf) of derivative instruments outstanding as of the balance sheet date qualifying as cash flow hedges.

No definition available.

Name:	swn_VolumeOfNaturalGasProductionInBcfCashFlowHedges
Namespace Prefix:	swn_
Data Type:	num:volumeItemType
Balance Type:	na
Period Type:	instant