v2.3.0.15

Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2006	Dec. 31, 2005
Related Party Transaction [Line Items]
Recognized net revenue	$ 123,290	$ 122,759	$ 359,035	$ 354,011
High Performance Partners LLC [Member]
Related Party Transaction [Line Items]
Business acquisition, contingent consideration	6,417		6,417
GE And Companies Where GE Has Majority Ownership Interest Or Exercises Significant Influence [Member]
Related Party Transaction [Line Items]
Minimum volume commitment							90,000	180,000	270,000	360,000	360,000	360,000	360,000	360,000	360,000	360,000
Extension of minimum volume commitment					90,000	150,000	250,000
Recognized net revenue	123,075	122,673	358,487	353,791
Percentage of total net revenue	29.00%	38.00%	31.00%	39.00%
Cost of revenue, net of recovery	680	960	2,747	3,542
Selling, general and administrative expenses recovery, net	26	107	308	420
Other operating (income) expense, net	(533)	(626)	(1,633)	(1,867)
Interest income from deposits	0	0	0	118
Interest expense on lease obligations	73	123	264	265
Customer In Which Company's Directors Have Controlling Interest [Member]
Related Party Transaction [Line Items]
Recognized net revenue	135	86	293	220
Customer Which Has Significant Interest In The Company [Member]
Related Party Transaction [Line Items]
Recognized net revenue	80	0	255	0
Non-Consolidating Affiliates [Member]
Related Party Transaction [Line Items]
Cost of revenue, net of recovery	588	318	945	897
Selling, general and administrative expenses recovery, net	122	97	118	397
Investment in equity affiliates	$ 0	$ 0	$ 0	$ 2,324

X

- Definition

Represents the minimum value of services to be purchased by related party over the extended period of contract.

+ Details

Name:	g_ExtensionOfMinimumVolumeCommitment
Namespace Prefix:	g
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Investment in equity affiliates where investment is between twenty and fifty percent with voting rights or more than twenty percent in other cases.

+ Details

Name:	g_InvestmentsInEquityAffiliates
Namespace Prefix:	g
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Represents the minimum value of services to be purchased by related party over the contracted period.

+ Details

Name:	g_MinimumVolumeCommitment
Namespace Prefix:	g
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Interest earned during the reporting period on deposits placed with related party.

+ Details

Name:	g_RelatedPartyTransactionInterestIncomeFromDeposits
Namespace Prefix:	g
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The total amount of other operating income and expense arising from entity's normal revenue producing operating transactions with related parties during the reporting period.

+ Details

Name:	g_RelatedPartyTransactionOtherOperatingIncomeAndExpense
Namespace Prefix:	g
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Net revenue from a related party as a percentage of total net revenues of the Company for the reporting period.

+ Details

Name:	g_RelatedPartyTransactionRevenuePercentageOfTotalRevenue
Namespace Prefix:	g
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Expenses recognized in selling, general and administrative expenses during the period resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ Details

Name:	g_RelatedPartyTransactionSellingGeneralAndAdministrativeExpenseFromTransactionsWithRelatedParty
Namespace Prefix:	g
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of potential cash payments that could result from the contingent consideration arrangement.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph f

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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

X

- Definition

The amount of interest expense incurred during the period on a debt or other obligation to a related party.

+ Details

Name:	us-gaap_InterestExpenseRelatedParty
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount included in cost of sales related to transactions with related parties incurred and recorded in the statement of operations for the period.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

-Paragraph 3

-Subparagraph b



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367646&loc=d3e18780-107790



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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.

+ Details

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

X

- Definition

Revenues, net of returns and allowances, realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 57

-Paragraph 2

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration