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Auction Rate Securities - Additional Information (Detail) $ in Millions	Mar. 31, 2017 USD ($)
Investments Debt And Equity Securities [Abstract]
Auction Rate Securities with fair value having no stated maturity	$ 1.5

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- Definition

Auction rate securities with fair value having no stated maturity.

+ References

No definition available.

+ Details

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Namespace Prefix:	syna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- References

No definition available.

+ Details

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