Derivatives and Risk Management (Cash Flow Hedges on Volumes of Natural Gas Production) (Details) (Fixed Price Swaps [Member])	Dec. 31, 2012
Year 2013 [Member]
Derivative [Line Items]
Volume of Natural Gas Production (in Bcf), Cash Flow Hedges	185.6
Year 2014 [Member]
Derivative [Line Items]
Volume of Natural Gas Production (in Bcf), Cash Flow Hedges	18.3

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:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant