v2.3.0.15

Short-Term Borrowings (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2011
Credit Facility Short Term Borrowings [Line Items]
Fund-based and non-fund-based credit facilities limit available	$ 20,560
Utilization of credit facility for non fund-based usage	4,082
Total utilization of revolving credit facility	259,133
Utilization of revolving credit facility for fund-based usage	252,000
Utilization of revolving credit facility for non-fund-based usage	7,133
Margin over LIBOR	1.65%
Revolving Credit Facility [Member]
Credit Facility Short Term Borrowings [Line Items]
Fund based and non-fund-based short term revolving credit facility maximum limit	$ 260,000
Revolving credit facility, expiration date	May 2015

X

- Definition

Credit Facility Short Term Borrowings [Line Items]

+ Details

Name:	g_CreditFacilityShortTermBorrowingsLineItems
Namespace Prefix:	g
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Limit available for fund based and non fund based credit facilities with banks for short term in the form of overdraft, letter of credit, guarantees, short term loans excluding forward hedging.

+ Details

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

X

- Definition

Maximum short term borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ Details

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

X

- Definition

This element represents the margin to be added to LIBOR to arrive at the interest rate to be paid on the credit facility.

+ Details

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

X

- Definition

This element represents the total utilization of revolving credit facility for both fund based and non-fund based usage for short term in the form of overdraft, letter of credit, guarantees, short term loans excluding forward hedging.

+ Details

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

X

- Definition

This element represents the utilization of credit facility for non-fund based usage for short term in the form of overdraft, letter of credit, guarantees, short term loans excluding forward hedging.

+ Details

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

X

- Definition

This element represents the utilization of revolving credit facility for fund based usage for short term in the form of overdraft, letter of credit, guarantees, short term loans excluding forward hedging.

+ Details

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

X

- Definition

This element represents the utilization of revolving credit facility for non-fund based usage for short term in the form of overdraft, letter of credit, guarantees, short term loans excluding forward hedging.

+ Details

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

X

- Definition

Reflects when the credit facility terminates, which may be presented in a variety of ways (year, month and year, day, month and year, quarter).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5



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

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

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate
Namespace Prefix:	us-gaap
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration