Document and Entity Information	3 Months Ended
	Mar. 31, 2018
Document And Entity Information [Abstract]
Document Type	S-1
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Trading Symbol	SPRO
Entity Registrant Name	Spero Therapeutics, Inc.
Entity Central Index Key	0001701108
Entity Filer Category	Non-accelerated Filer