XML 49 R38.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Share Based Payments - Summary of Non-Employee Stock Options Required to be Accounted for As Liabilities (Detail) - Non-employee Stock Options - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Fair value of non-employee options at beginning of period | $ 2,637 | $ 1,617
Exercise of non-employee options | (737) |
Change in fair value of non-employee stock options during the period | (571) | 162
Fair value of non-employee options at end of period | $ 1,329 | $ 1,779

X
- Definition Share-based compensation arrangement by share-based payment award options vested in non employee change in fair value. + References No definition available. + Details
Name: | hsdt_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInNonEmployeeChangeInFairValue
Namespace Prefix: | hsdt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Share based compensation arrangement by share based payment award options vested in period exercised. + References No definition available. + Details
Name: | hsdt_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriodExercised
Namespace Prefix: | hsdt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Share-based compensation arrangement by share-based payment award options vested in period fair value. + References No definition available. + Details
Name: | hsdt_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriodFairValue
Namespace Prefix: | hsdt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AwardTypeAxis=hsdt_NonEmployeeStockOptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |