Percentage Of Ownership Interests Acquired

No definition available.

Name:	hrst_PercentageOfOwnershipInterestsAcquired
Namespace Prefix:	hrst_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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

- Definition

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 55
-Paragraph 37
-URI http://asc.fasb.org/extlink&oid=116868840&loc=d3e2207-128464

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=116869197&loc=d3e4845-128472

+ Details

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

- Definition

The cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=srt_AffiliatedEntityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=hrst_EagleFordAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=hrst_CentralTexasAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

ACQUISITIONS (Narrative) (Details) - USD ($) $ in Thousands	5 Months Ended	7 Months Ended	12 Months Ended
ACQUISITIONS (Narrative) (Details) - USD ($) $ in Thousands	May 31, 2018	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2017	Aug. 31, 2017	Jan. 31, 2017
Business Acquisition [Line Items]
Proceeds from sale of oil and gas property and equipment	$ 3	$ 140,324	$ 119,750	$ 3,654
Affiliated Entity [Member]
Business Acquisition [Line Items]
Oil and natural gas properties acquired interest, percentage						87.00%
Eagle Ford Acquisition [Member]
Business Acquisition [Line Items]
Oil and natural gas properties acquired interest, percentage						5.80%
Oil and natural gas properties acquired, purchase price						$ 58,700
Central Texas [Member]
Business Acquisition [Line Items]
Oil and natural gas properties acquired interest, percentage					40.00%
Oil and natural gas properties acquired, purchase price					$ 2,700