Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-6

+ Details

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

- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards that are not subject to expiration dates.

+ References

+ Details

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

- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards that are subject to expiration dates.

+ References

+ Details

Name:	us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-3

+ Details

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

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=iclr_UnitedStatesFederalJurisdictionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=iclr_UnitedStatesStateJurisdictionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TaxPeriodAxis=iclr_TaxYear2026To2039Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TaxPeriodAxis=iclr_TaxYear20402045Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Income Taxes - Schedule of Expected Expiry Dates of NOL's (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Federal NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, not subject to expiration	$ 0
Net operating loss carryforwards	6,706	$ 8,000	$ 1,700
State NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, not subject to expiration	12,926
Net operating loss carryforwards	311,649	$ 277,800	$ 331,400
2026-2039 \| Federal NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	6,706
2026-2039 \| State NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	250,239
2040-2045 \| Federal NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	0
2040-2045 \| State NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	$ 48,484