Document and Entity Information - shares	6 Months Ended
	Dec. 31, 2017	Jan. 31, 2018
Document Documentand Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	MRCY
Entity Registrant Name	MERCURY SYSTEMS INC
Entity Central Index Key	0001049521
Current Fiscal Year End Date	--06-30
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		48,242,590