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Inventories - Additional Information (Detail) $ in Millions	6 Months Ended
	Dec. 31, 2019 USD ($)
Inventory Disclosure [Abstract]
Transfer of inventory to current assets held for sale	$ 20.9

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- Definition

Transfer of inventory to current assets held for sale.

+ References

No definition available.

+ Details

Name:	syna_TransferOfInventoryToCurrentAssetsHeldForSale
Namespace Prefix:	syna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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- References

No definition available.

+ Details

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