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Common Stock and Warrants - Summary of Weighted Average Assumptions Used in Estimating Fair Value of Warrants (Details)	Feb. 01, 2021 $ / shares	Dec. 31, 2020 $ / shares	Oct. 26, 2020 $ / shares	Mar. 20, 2020 $ / shares	Apr. 24, 2018 $ / shares	Apr. 13, 2018 $ / shares
Outsiders
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price			$ 15.92
Exercise price			$ 15.92
Warrant Term | Outsiders
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term			3 years
Expected Volatility | Outsiders
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input			80.91
Risk-Free Interest Rate | Outsiders
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input			0.18
Dividend Rate | Outsiders
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input			0.00
April 2018 Offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Exercise price						$ 428.75
February 2021 Offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Exercise price	$ 16.302
Warrants Granted | April 2018 Offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price					$ 376.60	344.75
Exercise price					$ 428.75	$ 428.75
Warrants and Rights Outstanding, Type [Extensible List]					hsdt:BlackScholesOptionPricingModelMember	hsdt:BlackScholesOptionPricingModelMember
Warrants Granted | April 2018 Offering | Warrant Term
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term					3 years	3 years
Warrants Granted | April 2018 Offering | Expected Volatility
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input					64.49	64.20
Warrants Granted | April 2018 Offering | Risk-Free Interest Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input					2.02	1.99
Warrants Granted | April 2018 Offering | Dividend Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input					0.00	0.00
Warrants Granted | March 2020 Offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price				$ 12.25
Exercise price				$ 16.10
Warrants and Rights Outstanding, Type [Extensible List]				hsdt:BlackScholesOptionPricingModelMember
Warrants Granted | March 2020 Offering | Warrant Term
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term				5 years 6 months
Warrants Granted | March 2020 Offering | Expected Volatility
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input				82.41
Warrants Granted | March 2020 Offering | Risk-Free Interest Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input				0.52
Warrants Granted | March 2020 Offering | Dividend Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input				0.00
Warrants Granted | February 2021 Offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price	14.82
Exercise price	$ 16.47
Warrants and Rights Outstanding, Type [Extensible List]	hsdt:BlackScholesOptionPricingModelMember
Warrants Granted | February 2021 Offering | Warrant Term
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term	5 years
Warrants Granted | February 2021 Offering | Expected Volatility
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input	75.02
Warrants Granted | February 2021 Offering | Risk-Free Interest Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input	0.42
Warrants Granted | February 2021 Offering | Dividend Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input	0.00
Warrant | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price		$ 17.15
Exercise price		$ 428.75
Warrants and Rights Outstanding, Type [Extensible List]		hsdt:BlackScholesOptionPricingModelMember
Warrant | Warrant Term | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term		3 months 7 days
Warrant | Expected Volatility | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input		64.48
Warrant | Risk-Free Interest Rate | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input		0.06
Warrant | Dividend Rate | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input		0.00

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- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-Topic 820
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+ References

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-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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