Debt Instrument, Issue Price, Percent

No definition available.

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Redemption Price, Percentage of Principal Amount That May Be Redeemed

+ References

No definition available.

+ Details

Name:	it_DebtInstrumentRedemptionPricePercentageofPrincipalAmountThatMayBeRedeemed
Namespace Prefix:	it_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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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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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
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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
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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

+ Details

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

- Definition

The cash outflow for a borrowing having initial term of repayment within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

+ Details

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

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_BridgeLoanMember
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Debt - Bridge Facility and Senior Notes (Details) - USD ($) $ in Millions			12 Months Ended
	Apr. 05, 2017	Mar. 30, 2017	Dec. 31, 2017
Senior notes
Debt Instrument [Line Items]
Proceeds from issuance of debt		$ 800.0
CEB
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 2,800.0
CEB \| Senior notes
Debt Instrument [Line Items]
Proceeds from issuance of debt		$ 800.0
Debt instrument, fixed interest rate		5.125%
Issue price, percent		100.00%
Redeemable percentage of principal amount		40.00%
CEB \| Senior notes \| Redemption period one
Debt Instrument [Line Items]
Redemption price percentage		105.125%
CEB \| Senior notes \| Redemption period two
Debt Instrument [Line Items]
Redemption price percentage		100.00%
CEB \| Senior notes \| Redemption period three
Debt Instrument [Line Items]
Redemption price percentage		101.00%
Bridge Loan \| CEB
Debt Instrument [Line Items]
Debt instrument term	364 days		364 days
Proceeds from issuance of debt	$ 300.0
Repayments of short-term debt			$ 300.0