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Other Balance Sheet Items (Details) $ in Millions	Dec. 31, 2019 USD ($)
Disclosure Text Block Supplement [Abstract]
Convertible note for the sale of assets	$ 2.1

X

- Definition

Convertible note.

+ References

No definition available.

+ Details

Name:	hlgn_ConvertiblesNote
Namespace Prefix:	hlgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- References

No definition available.

+ Details

Name:	us-gaap_DisclosureTextBlockSupplementAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration