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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
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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 + Details
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