Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Aug. 07, 2018
Entity Registrant Name	Federal Street Acquisition Corp.
Entity Central Index Key	0001701821
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Class A Common Stock
Entity Common Stock, Shares Outstanding		46,000,000
Class F Common Stock
Entity Common Stock, Shares Outstanding		11,500,000