Percentage of total debt to total capitalization of the entity.

No definition available.

Name:	hp_DebtInstrumentPercentageTotalDebtToTotalCapitalization
Namespace Prefix:	hp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of letters of credit outstanding as of balance sheet date.

+ References

No definition available.

+ Details

Name:	hp_LettersOfCreditOutstandingNumber
Namespace Prefix:	hp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the maximum percentage of priority debt that can be allowed on the net worth of the entity.

+ References

No definition available.

+ Details

Name:	hp_MaximumLimitOfPriorityDebtOnNetWorth
Namespace Prefix:	hp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of letters of credit that were decreased.

+ References

No definition available.

+ Details

Name:	hp_NumberOfLettersCreditDecreased
Namespace Prefix:	hp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Amount of increase (decrease) of the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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Balance Type:
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- Details

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Data Type:	na
Balance Type:
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- Details

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- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
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- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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- Details

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DEBT - Debt activity (Details)			1 Months Ended	12 Months Ended
DEBT - Debt activity (Details)	Jul. 13, 2016 USD ($)	Mar. 19, 2015 USD ($)	Nov. 13, 2018 USD ($) letter	Sep. 30, 2018 USD ($) letter	Sep. 30, 2017 USD ($)
Debt
Face Amount				$ 500,000,000	$ 500,000,000
Unsecured senior notes issued March 19, 2015
Debt
Face Amount		$ 500,000,000		$ 500,000,000	$ 500,000,000
Long-term debt stated interest rate percentage		4.65%
Term of debt		10 years
2016 Credit Facility
Debt
Maximum borrowing capacity	$ 300,000,000
Commitment fee (as a percent)				0.15%
Maximum limit of priority debt on net worth				17.50%
Borrowing amount outstanding				$ 0
Available borrowing capacity				$ 260,700,000
2016 Credit Facility \| Minimum
Debt
Commitment fee (as a percent)	0.15%
2016 Credit Facility \| Maximum
Debt
Commitment fee (as a percent)	0.30%
Total debt to total capitalization (as a percent)	50.00%
2016 Credit Facility \| London Interbank Offered Rate (LIBOR)
Debt
Interest spread on borrowings (as a percent)				1.125%
2016 Credit Facility \| London Interbank Offered Rate (LIBOR) \| Minimum
Debt
Interest spread on borrowings (as a percent)	1.125%
2016 Credit Facility \| London Interbank Offered Rate (LIBOR) \| Maximum
Debt
Interest spread on borrowings (as a percent)	1.75%
2016 Credit Facility \| Letters of credit
Debt
Maximum borrowing capacity	$ 75,000,000
Number of letters of credit outstanding \| letter				3
Letters of credit outstanding/issued				$ 39,300,000
2016 Credit Facility \| Issued to support self-insured losses under high deductible casualty insurance programs
Debt
Number of letters of credit outstanding \| letter				2
Letters of credit outstanding/issued				$ 29,300,000
2016 Credit Facility \| Letter of credit supporting an operating line of credit with a bank in Argentina
Debt
Letters of credit outstanding/issued				10,000,000
2016 Credit Facility \| Subsequent Event
Debt
Available borrowing capacity			$ 262,000,000
Decrease in credit facility			$ 300,000,000
2016 Credit Facility \| Subsequent Event \| Letters of credit
Debt
Number of letters of credit decreased \| letter			1
Decrease in credit facility			$ 1,300,000
2018 Credit Facility \| Subsequent Event
Debt
Maximum borrowing capacity			750,000,000
Borrowing amount outstanding			0
Letters of credit outstanding/issued			3
Available borrowing capacity			$ 712,000,000
2018 Credit Facility \| Subsequent Event \| Forecast
Debt
Commitment fee (as a percent)			0.125%
2018 Credit Facility \| Subsequent Event \| Minimum
Debt
Commitment fee (as a percent)			0.075%
2018 Credit Facility \| Subsequent Event \| Maximum
Debt
Commitment fee (as a percent)			0.20%
Total debt to total capitalization (as a percent)			50.00%
2018 Credit Facility \| Subsequent Event \| London Interbank Offered Rate (LIBOR) \| Forecast
Debt
Interest spread on borrowings (as a percent)			1.125%
2018 Credit Facility \| Subsequent Event \| London Interbank Offered Rate (LIBOR) \| Minimum
Debt
Interest spread on borrowings (as a percent)			0.875%
2018 Credit Facility \| Subsequent Event \| London Interbank Offered Rate (LIBOR) \| Maximum
Debt
Interest spread on borrowings (as a percent)			1.50%
2018 Credit Facility \| Subsequent Event \| Letters of credit
Debt
Maximum borrowing capacity			$ 75,000,000
Letters of credit outstanding/issued			$ 38,000,000
Unsecured standalone line of credit facility
Debt
Maximum borrowing capacity				$ 12,000,000