Name:	gk_LongTermDebtMaturitiesRepaymentsOfPrincipalIncludingCapitalLeasesInNextTwelveMonths
Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of long-term debt, sinking fund requirements, capital lease obligations, and other securities redeemable at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year and thereafter.

No definition available.

Name:	gk_LongTermDebtMaturitiesRepaymentsOfPrincipalIncludingCapitalLeasesInYearFiveAndThereafter
Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of long-term debt, sinking fund requirements, capital lease obligations, and other securities redeemable at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year.

No definition available.

Name:	gk_LongTermDebtMaturitiesRepaymentsOfPrincipalIncludingCapitalLeasesInYearFour
Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of long-term debt, sinking fund requirements, capital lease obligations, and other securities redeemable at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year.

No definition available.

Name:	gk_LongTermDebtMaturitiesRepaymentsOfPrincipalIncludingCapitalLeasesInYearThree
Namespace Prefix:	gk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of long-term debt, sinking fund requirements, capital lease obligations, and other securities redeemable at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year.

No definition available.