v3.8.0.1
Document and Entity Information - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Mar. 07, 2018
Jun. 30, 2017
Document and Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
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    
Class of Stock [Line Items]      
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 215
Common Class A      
Class of Stock [Line Items]      
Entity Common Stock, Shares Outstanding   13,135,636  
Common Class B      
Class of Stock [Line Items]      
Entity Common Stock, Shares Outstanding   21,485,126