Document and Entity Information Document	3 Months Ended
	Mar. 31, 2013	Apr. 25, 2013
Entity Information [Line Items]
Entity Registrant Name	SM Energy Co
Entity Central Index Key	0000893538
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		66,275,824
Entity Current Reporting Status	Yes