Inventory - Additional Information (Details) $ in Thousands	12 Months Ended
Jun. 30, 2019 USD ($)
Inventory Disclosure [Abstract]
Increase in inventory	$ 28,527

Increase (Decrease) In Inventories Including Assets Acquired

No definition available.

Name:	mrcy_IncreaseDecreaseInInventoriesIncludingAssetsAcquired
Namespace Prefix:	mrcy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration