Cash bonus award determination percentage on achievement of patient enrollment levels maximum target level

No definition available.

Name:	hznp_CashBonusAwardDeterminationPercentageOnAchievementOfPatientEnrollmentLevelsMaximumTargetLevel
Namespace Prefix:	hznp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Employee service share based compensation tax benefit (detriment) from compensation expense.

+ References

No definition available.

+ Details

Name:	hznp_EmployeeServiceShareBasedCompensationTaxBenefitDetrimentFromCompensationExpense
Namespace Prefix:	hznp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sharebased compensation arrangement by sharebased payment award award percentage of net sales performance criteria met.

+ References

No definition available.

+ Details

Name:	hznp_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardPercentageOfNetSalesPerformanceCriteriaMet
Namespace Prefix:	hznp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of commitment made to pay deferred cash remuneration.

+ References

No definition available.

+ Details

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

- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

+ Details

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

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

+ Details

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

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of additional shares authorized for issuance under share-based payment arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

+ Details

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

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

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

- Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis=us-gaap_DeferredBonusMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=hznp_TEPEZZAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=hznp_MembersOfExecutiveCommitteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=hznp_TwoThousandFourteenEmployeeSharePurchasePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=hznp_TwoThousandFourteenEquityIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=hznp_TwoThousandFourteenNonEmployeeStockPurchasePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Share-Based and Long-Term Incentive Plans - Additional Information (Detail) - USD ($) $ in Millions			3 Months Ended		12 Months Ended
	Mar. 31, 2020	Feb. 19, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jan. 05, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options contractual term			10 years
Tax benefit (detriment) recognized from stock-based compensation expense			$ 14.1	$ 2.5
Pre-tax unrecognized compensation expense for all unvested share-based awards	$ 178.1		$ 178.1
Cash Incentive Program [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			36 months
Bonus payable under cash bonus program						$ 14.1
Cash bonus award maximum target level			150.00%
Expense related to cash bonus program			$ 1.0	$ 1.2
Performance Stock Unit Awards [Member] \| TEPEZZA [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding PSU award vesting amount range	50.00%
Vesting period	1 year
PSUs outstanding	724,490		724,490
Performance Stock Unit Awards [Member] \| TEPEZZA [Member] \| Members of Executive Committee [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding PSU award vesting amount range	33.00%
Performance Stock Unit Awards [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding PSU award vesting amount range			0.00%
Performance Stock Unit Awards [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding PSU award vesting amount range			200.00%
Performance Stock Unit Awards [Member] \| Relative TSR PSUs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding PSU award vesting amount range			30.00%		30.00%
Vesting period			3 years		3 years
Performance Stock Unit Awards [Member] \| Net Sales PSUs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of outstanding PSU award vesting amount range			70.00%		70.00%
Percentage of net sales performance criteria met					119.20%
2014 ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized	1,236,775		1,236,775
Common stock shares reserved for future issuance	1,236,775		1,236,775
Increase to number of ordinary shares authorized		2,500,000
2014 EIP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized	5,612,651		5,612,651
Common stock shares reserved for future issuance	5,612,651		5,612,651
Common stock shares available for grant	532,737		532,737
Increase to number of ordinary shares authorized		6,900,000
2014 Non-Employee Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized	698,491		698,491
Common stock shares reserved for future issuance	698,491		698,491