Commitments and Contingencies - Schedule of Aggregate Undiscounted Minimum Future Lease Payments (Detail) - Lease Financing Obligation [Member] $ in Thousands	Dec. 31, 2018 USD ($)
Future Minimum Lease Payments Under Capital Leases And Operating Leases For Continuing Operations [Line Items]
2019	$ 1,869
Thereafter	0
Total	$ 1,869

Future Minimum Lease Payments Under Capital Leases And Operating Leases For Continuing Operations [Line Items]

No definition available.

Name:	hpr_FutureMinimumLeasePaymentsUnderCapitalLeasesAndOperatingLeasesForContinuingOperationsLineItems
Namespace Prefix:	hpr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of minimum lease payments for capital leases.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737

+ Details

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

- Definition

Amount of minimum lease payments for capital leases due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of minimum lease payments for capital leases due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=hpr_FinancingObligationsAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: