Changes in Carrying Amount of Goodwill (Detail) $ in Thousands	3 Months Ended
Sep. 27, 2019 USD ($)
Goodwill [Roll Forward]
Beginning Balance	$ 562,146
Ending Balance	617,175
SMP
Goodwill [Roll Forward]
Beginning Balance	140,783
Ending Balance	195,365
AMS
Goodwill [Roll Forward]
Beginning Balance	222,379
Ending Balance	222,379
MDS
Goodwill [Roll Forward]
Beginning Balance	198,984
Ending Balance	199,431
Germane Systems
Goodwill [Roll Forward]
Goodwill arising from acquisitions	(447)
Germane Systems \| MDS
Goodwill [Roll Forward]
Goodwill arising from acquisitions	(447)
GECO Avionics, LLC
Goodwill [Roll Forward]
Goodwill arising from acquisitions	(200)
GECO Avionics, LLC \| SMP
Goodwill [Roll Forward]
Goodwill arising from acquisitions	(200)
GECO Avionics, LLC \| AMS
Goodwill [Roll Forward]
Goodwill arising from acquisitions	0
GECO Avionics, LLC \| MDS
Goodwill [Roll Forward]
Goodwill arising from acquisitions	$ 0

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mrcy_SensorAndMissionProcessingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mrcy_AdvancedMicroelectronicSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mrcy_MercuryDefenseSystemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=mrcy_GermaneSystemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=mrcy_GECOAvionicsLLCMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: