Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2018	Jul. 31, 2018	Dec. 31, 2017
Document Documentand Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	MRCY
Entity Registrant Name	MERCURY SYSTEMS INC
Entity Central Index Key	0001049521
Current Fiscal Year End Date	--06-30
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		48,221,418
Entity Public Float			$ 2,500.0