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Basis of Presentation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Net gain (loss) on foreign currency transactions	$ (0.2)	$ (0.2)	$ (0.6)	$ (0.5)

X

- Definition

Foreign currency transaction realized and unrealized gain (loss) net of tax.

+ References

No definition available.

+ Details

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Namespace Prefix:	syna_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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- References

No definition available.

+ Details

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