Description of Business (Details)	3 Months Ended
Sep. 30, 2018 program contractor
Accounting Policies [Abstract]
Number of programs using products and services \| program	300
Number of defense prime contractors using products and services \| contractor	25

Nature of Business, Number of Contractors Using Products and Services

No definition available.

Name:	mrcy_NatureofBusinessNumberofContractorsUsingProductsandServices
Namespace Prefix:	mrcy_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration