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v3.20.4

Accrued Expenses - Additional Information (Details) $ in Millions | Dec. 31, 2020 USD ($)
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Chief Executive Officer |
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items] |
Accrued Severance Cost | $ 0.3

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- Definition Accrued severance cost. + References No definition available. + Details
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Namespace Prefix: | hsdt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
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Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |