v3.25.3

Leases - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Leases - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Lessee, Lease, Description [Line Items]
Renewal term (in years)	10 years		10 years
Option to terminate, term (in years)			1 year
Loss on impairment of lease related assets, net			$ 4,702	$ 2,950
Selling, general and administrative
Lessee, Lease, Description [Line Items]
Loss on impairment of lease related assets, net	$ 4,100	$ 2,400	$ 4,700	$ 3,000

Lessee, Operating Lease, Option to Terminate, Term

+ References

No definition available.

+ Details

Name:	it_LesseeOperatingLeaseOptiontoTerminateTerm
Namespace Prefix:	it_
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7A
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-7A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ Details

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

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ Details

Name:	us-gaap_LesseeOperatingLeaseRenewalTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of loss from impairment of right-of-use asset from operating lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479365/842-20-25-6

+ Details

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

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

GARTNER INC 10-Q