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Fair Value Instruments (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Fair Value Disclosures [Abstract]
Liability warrants	$ 46

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- References

No definition available.

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

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- References

No definition available.

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Namespace Prefix:	us-gaap_
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