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Common Stock and Warrants - Summary of Weighted Average Assumptions Used in Estimating Fair Value of Warrants (Details)	Dec. 31, 2020 $ / shares	Oct. 26, 2020 $ / shares	Mar. 20, 2020 $ / shares	Dec. 31, 2019 $ / shares	Apr. 24, 2018 $ / shares	Apr. 13, 2018 $ / shares
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
Outsiders [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price		$ 15.92
Exercise price		$ 15.92
Warrants | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price				$ 43.05
Exercise price				$ 428.75
Warrants And Rights Outstanding Type Extensible List				hsdt:BlackScholesOptionPricingModelMember
April 2018 Offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Exercise price						$ 428.75
April 2018 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock price	17.15				$ 4,376.60	344.75
Exercise price	$ 428.75				$ 428.75	$ 428.75
Warrants And Rights Outstanding Type Extensible List	hsdt:BlackScholesOptionPricingModelMember				hsdt:BlackScholesOptionPricingModelMember	hsdt:BlackScholesOptionPricingModelMember
March 2020 Offering | Warrants Granted
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
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 Term | Outsiders [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term		3 years
Warrant Term | Warrants | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term				1 year 3 months 10 days
Warrant Term | April 2018 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term	3 months 7 days				3 years	3 years
Warrant Term | March 2020 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, term			5 years 6 months
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
Expected Volatility | Outsiders [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input		80.91
Expected Volatility | Warrants | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input				72.43
Expected Volatility | April 2018 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input	64.48				64.49	64.20
Expected Volatility | March 2020 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input			82.41
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
Risk-Free Interest Rate | Outsiders [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input		0.18
Risk-Free Interest Rate | Warrants | Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input				1.72
Risk-Free Interest Rate | April 2018 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input	0.06				2.02	1.99
Risk-Free Interest Rate | March 2020 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input			0.52
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
Dividend Rate | Outsiders [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input		0.00
Dividend Rate | Warrants | 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
Dividend Rate | April 2018 Offering | Warrants Granted
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Weighted average assumptions, measurement input	0.00				0.00	0.00
Dividend Rate | March 2020 Offering | Warrants Granted
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
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+ References

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