Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2018
Entity Registrant Name	SemGroup Corp
Entity Central Index Key	0001489136
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Common Class A [Member]
Entity Common Stock, Shares Outstanding		79,029,331
Class B
Entity Common Stock, Shares Outstanding		0