Billing cycle period.

No definition available.

Name:	g_BillingCyclePeriod
Namespace Prefix:	g_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Disposal Group Including Discontinued Operation, Contract Assets

+ References

No definition available.

+ Details

Name:	g_DisposalGroupIncludingDiscontinuedOperationContractAssets
Namespace Prefix:	g_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Disposal Group Including Discontinued Operation, Contract Cost Assets, Current

+ References

No definition available.

+ Details

Name:	g_DisposalGroupIncludingDiscontinuedOperationContractCostAssetsCurrent
Namespace Prefix:	g_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Disposal Group Including Discontinued Operation, Contract Liabilities, Current

+ References

No definition available.

+ Details

Name:	g_DisposalGroupIncludingDiscontinuedOperationContractLiabilitiesCurrent
Namespace Prefix:	g_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of revenue recognized that was previously reported as deferred or unearned revenue.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredRevenueRevenueRecognized1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

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

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8672-108599

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Period in which remaining performance obligation is expected to be recognized as revenue, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130556-203045

+ Details

Name:	us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis=2023-04-01
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis=2025-01-01
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis=2027-01-01
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis=2029-01-01
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=g_TheBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Net Revenues - Narrative (Detail) $ in Thousands	3 Months Ended
Net Revenues - Narrative (Detail) $ in Thousands	Mar. 31, 2023 USD ($) numberOfOperatingSegment	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments \| numberOfOperatingSegment	3
Billing cycle period	30 days
Revenue recognized	$ 71,504	$ 46,625
Revenue, remaining performance obligation, expected timing of satisfaction, start date [Axis]: 2023-04-01
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	9 months
Revenue, remaining performance obligation, expected timing of satisfaction, start date [Axis]: 2025-01-01
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	3 years
Revenue, remaining performance obligation, expected timing of satisfaction, start date [Axis]: 2027-01-01
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	3 years
Revenue, remaining performance obligation, expected timing of satisfaction, start date [Axis]: 2029-01-01
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period
Disposal group, held-for-sale, not discontinued operations
Disaggregation of Revenue [Line Items]
Disposal group including discontinued operation, contract assets	$ 0		$ 2,168
Contract liabilities held for sale	0		649
Disposal group, held-for-sale, not discontinued operations \| The Business
Disaggregation of Revenue [Line Items]
Disposal group including discontinued operation, contract cost assets	$ 0		$ 1,247