Debt (Details) - USD ($)	1 Months Ended
May 31, 2020	Jan. 31, 2020
Debt Instrument [Line Items]
Proceeds from Paycheck Protection Program loan	$ 900,000
Convertible notes payable \| January 2020 Note
Debt Instrument [Line Items]
Cash proceeds from debt		$ 3,200,000
Interest rate		6.00%
Debt term		5 years
Optional conversion, equity financing (at least)		$ 15,000,000
Conversion price, discount from equity financing share price		50.00%
Optional conversion, change in control, conversion price, purchase price multiplier		50.00%
Optional conversion, minimum amount of new commercial debt		$ 10,000,000
Event of default, additional interest rate		3.00%
Event of default, interest rate		9.00%
Debt term optional extension		5 years
Interest rate if not converted		4.00%
Fair value of conversion features		$ 2,700,000

Debt Instrument, Additional Interest Rate Upon Event Of Default, Stated Percentage

No definition available.

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- Definition

Debt Instrument, Convertible, Optional Redemption, Conversion Price, Change In Control, Purchase Price Multiplier

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Convertible, Optional Redemption, Conversion Price, Discount

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Convertible, Optional Redemption, Minimum Amount of Equity Financing Proceeds

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Debt Instrument, Convertible, Optional Redemption, Minimum Amount Of New Commercial Debt

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Interest Rate If No Conversion, Stated Percentage

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Interest Rate Upon Event Of Default, Stated Percentage

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Term Extension

+ References

No definition available.

+ Details

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- Definition

Proceeds From Paycheck Protection Program Loan

+ References

No definition available.

+ Details

Name:	hyln_ProceedsFromPaycheckProtectionProgramLoan
Namespace Prefix:	hyln_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of a favorable spread to a debt holder between the amount of debt being converted and the value of the securities received upon conversion. This is an embedded conversion feature of convertible debt issued that is in-the-money at the commitment date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21538-112644

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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- 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

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

The cash inflow from the issuance of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

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Balance Type:	debit
Period Type:	duration

- Details

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- Details

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