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Leases - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2023 | Mar. 31, 2022
Lessee, Lease, Description [Line Items] |  |
Renewal term | 10 years |
Option to terminate, term | 1 year |
Loss on impairment of lease related assets, net | $ 8,720 | $ 23,878
Right-of-use Assets |  |
Lessee, Lease, Description [Line Items] |  |
Loss on impairment of lease related assets, net | 6,300 | 17,700
Leasehold Improvements |  |
Lessee, Lease, Description [Line Items] |  |
Loss on impairment of lease related assets, net | 2,400 | 6,200
Selling, general and administrative |  |
Lessee, Lease, Description [Line Items] |  |
Loss on impairment of lease related assets, net | $ 8,700 | $ 23,900

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- Definition Lessee, Operating Lease, Option to Terminate, Term + References No definition available. + Details
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Namespace Prefix: | it_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- 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
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Data Type: | xbrli:stringItemType
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Period Type: | duration

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- 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 -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980 + Details
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Namespace Prefix: | us-gaap_
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Period Type: | instant

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- Definition Amount of loss from impairment of right-of-use asset from operating lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 25 -Paragraph 6 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=123399704&loc=SL77918431-209957 + Details
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Namespace Prefix: | us-gaap_
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |