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Share Based Payments - Summary of Company's Restricted Stock Unit Activity (Parenthetical) (Details) | 12 Months Ended
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Dec. 31, 2019 shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Number of RSUs withheld for taxes | 7

X
- Definition Number of restricted stock units withheld for taxes. + References No definition available. + Details
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Namespace Prefix: | hsdt_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration