Borrowings (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2011
Debt Instrument [Line Items]
Revolver, available borrowing capacity	371.9
Base fixed rate	2.26%
Notional fixed-for-floating interest rate swap contract	200.0
Annualized effective interest rate, including impact of the swap	3.76%
Term Loan
Debt Instrument [Line Items]
Eurodollar base rate	0.37%
Margin	1.50%
Revolver
Debt Instrument [Line Items]
Eurodollar base rate	0.30%
Margin	1.50%

Debt Instrument Interest Additional Interest Above Base Rate

Name:	it_DebtInstrumentInterestAdditionalInterestAboveBaseRate
Namespace Prefix:	it
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument Interest Base Rate

+ Details

Name:	it_DebtInstrumentInterestBaseRate
Namespace Prefix:	it
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-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

Name:	us-gaap_DebtInstrumentInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
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.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fixed interest rate related to the interest rate derivative.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Aggregate notional amount of interest rate derivatives, which relates to the currency amount specified in the interest rate derivative instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5579245-113959

+ Details

Name:	us-gaap_NotionalAmountOfInterestRateDerivatives
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant