Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2019	Jul. 31, 2019	Dec. 31, 2018
Document Documentand Entity Information [Abstract]
Title of 12(b) Security	Common Stock, Par Value $0.01 Per Share
Entity Incorporation, State or Country Code	MA
Document Transition Report	false
Document Annual Report	true
Document Type	10-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Entity File Number	0-23599
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	MRCY
Entity Registrant Name	MERCURY SYSTEMS, INC
City Area Code	978
Local Phone Number	256-1300
Entity Central Index Key	0001049521
Current Fiscal Year End Date	--06-30
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		55,427,087
Entity Public Float			$ 2,300.0
Entity Tax Identification Number	04-2741391
Entity Address, Address Line One	50 Minuteman Road
Entity Address, Postal Zip Code	01810
Entity Address, City or Town	Andover
Entity Address, State or Province	MA
Security Exchange Name	NASDAQ