Name:	hlgn_ContractLiabilities
Namespace Prefix:	hlgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Contract with Customer, Liability, Increase for Deferred Revenue Additions

No definition available.

Name:	hlgn_ContractWithCustomerLiabilityIncreaseForDeferredRevenueAdditions
Namespace Prefix:	hlgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Contract with Customer, Liability, Revenue Recognized, Excluding Opening Balance

No definition available.

Name:	hlgn_ContractWithCustomerLiabilityRevenueRecognizedExcludingOpeningBalance
Namespace Prefix:	hlgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Loss on Contracts, Amortization

No definition available.

Name:	hlgn_LossOnContractsAmortization
Namespace Prefix:	hlgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Cumulative provision for contract losses not offset against related costs accumulated on the balance sheet.

No definition available.

Name:	hlgn_ProvisionForContractLoss
Namespace Prefix:	hlgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount, after allowance, receivable from customers, clients, or other third-parties, and receivables classified as other due within one year or the normal operating cycle, if longer.

No definition available.

Name:	us-gaap_AccountsAndOtherReceivablesNetCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4531-111522

Name:	us-gaap_AccountsReceivableNetCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

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

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130556-203045

Name:	us-gaap_RevenueRemainingPerformanceObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements due within one year or the normal operating cycle, if longer.

No definition available.