XML 74 R60.htm IDEA: XBRL DOCUMENT
v3.20.4

Debt - Interest Rate Swaps (Details) |  | 12 Months Ended |
--- | --- | --- | ---
Jun. 30, 2020 USD ($) | Dec. 31, 2020 USD ($) outstanding_contract loan | Dec. 31, 2019 USD ($) outstanding_contract | Dec. 31, 2018 USD ($) | Jun. 22, 2020 USD ($)
Derivative [Line Items] |  |  |  |  |
Number of contracts | outstanding_contract |  | 167 | 180 |  |
Contract notional amount |  | $ 1,830,063,000 | $ 2,004,858,000 |  |
Repayments of long-term debt |  | 2,058,469,000 | 102,579,000 | $ 570,972,000 |
Variable rate debt |  | 200,000,000.0 |  |  |
Senior Notes | Senior Notes Due 2028 |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Aggregate principal amount |  | $ 800,000,000.0 |  |  | $ 800,000,000
Secured Debt | Term Loan A | 2016 Credit Facility Agreement |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Repayments of long-term debt | $ 787,900,000 |  |  |  |
Interest rate swap |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Number of contracts | loan |  | 4 |  |  |
Contract notional amount |  | $ 1,400,000,000 |  |  |
Derivative, term of contract |  | 30 days |  |  |
Loss on release of interest rate swap recognized in AOCI |  | $ 104,000,000.0 |  |  |
Interest rate derivative hedge, asset (liability), net |  | 109,200,000 | 64,800,000 |  |
Interest rate swap | Other Expense |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Loss on release of interest rate swap recognized in earnings |  | 10,300,000 |  |  |
Interest rate swap | Accumulated Other Comprehensive (Loss) Income, Net |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Interest rate derivative hedge, asset (liability), net |  | $ 78,100,000 | $ 47,200,000 |  |
Interest rate swap | Minimum |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, fixed interest rate |  | 2.13% |  |  |
Interest rate swap | Maximum |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, fixed interest rate |  | 3.04% |  |  |

X
- Definition Debt Instrument, Expected Variable Rate Debt With No Interest Payments + References No definition available. + Details
Name: | it_DebtInstrumentExpectedVariableRateDebtWithNoInterestPayments
Namespace Prefix: | it_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after tax, of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580 + Details
Name: | us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fixed interest rate related to the interest rate derivative. + References No definition available. + Details
Name: | us-gaap_DerivativeFixedInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- 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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Nominal or face amount used to calculate payment on derivative. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959 + Details
Name: | us-gaap_DerivativeNotionalAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of derivative instruments of a particular group held by the entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959 + Details
Name: | us-gaap_DerivativeNumberOfInstrumentsHeld
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Period the derivative contract is outstanding, 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_DerivativeTermOfContract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of all derivatives designated as interest rate fair value hedging instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958 + Details
Name: | us-gaap_InterestRateFairValueHedgeDerivativeAtFairValueNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e689-108580 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash outflow for debt initially having maturity due after one year or beyond 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=121586364&loc=d3e3291-108585 + Details
Name: | us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=it_SeniorNotesDue2028Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CreditFacilityAxis=us-gaap_SecuredDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=it_BankTermLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=it_A2016CreditFacilityAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_OtherExpenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherComprehensiveIncomeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |