Expiration date of original contract.

No definition available.

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Namespace Prefix:	hsdt_
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- Definition

Expiration year of original contract.

+ References

No definition available.

+ Details

Name:	hsdt_ExpirationYearOfOriginalContract
Namespace Prefix:	hsdt_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Extended expiration date of original contract.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Reimbursement revenue recorded as advance milestone payment.

+ References

No definition available.

+ Details

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Namespace Prefix:	hsdt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Schedule of cost sharing agreement.

+ References

No definition available.

+ Details

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- Definition

Cost associated with reimbursable income. This occurs when a services entity incurs expenses on behalf of the client and passes through the cost of reimbursable expenses to a client.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Repayment received or receivable for expenses incurred on behalf of a client or customer, other than those reimbursements received by landlords from tenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 45
-Section 45
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=68075638&loc=d3e60722-111653

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
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- Details

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Sole-Source Cost-Sharing Agreement - Additional Information (Detail) - USAMRMC - USD ($)		1 Months Ended	3 Months Ended
	Nov. 07, 2017	Jul. 31, 2015	Mar. 31, 2018	Sep. 30, 2017
Schedule Of Cost Sharing Agreement [Line Items]
Expiration date of original contract			Dec. 31, 2016
Reimbursement received			$ 3,000,000
Reimbursement received recorded as advance against final milestone			$ 200,000
Extended expiration date of original contract	Dec. 31, 2018
Maximum
Schedule Of Cost Sharing Agreement [Line Items]
Reimbursable trial cost		$ 3,000,000
Cooperative Research and Development Agreement
Schedule Of Cost Sharing Agreement [Line Items]
Extended expiration date of original contract				Dec. 31, 2021
Expiration year of original contract				2018