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Basis of Presentation - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2018 | Mar. 31, 2017
Accounting Policies [Abstract] |  |  |  |
Net gain (loss) on foreign currency transactions | $ (0.3) | $ (0.4) | $ (0.8) | $ (0.4)

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