Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Aug. 01, 2018
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	SPKE
Entity Registrant Name	Spark Energy, Inc.
Entity Central Index Key	0001606268
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Common Class A
Class of Stock [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		13,393,712
Common Class B
Class of Stock [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		21,485,126