Name:	gk_ActualMinimumInterestCoverageRatio
Namespace Prefix:	gk_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

The actual leverage ratio is calculated as the ratio of total debt including letters of credit as of the reporting period date as compared to trailing twelve month consolidated total EBITDA.

No definition available.

Name:	gk_LeverageRatioActualMaximum
Namespace Prefix:	gk_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

The required maximum leverage ratio is calculated as the ratio of total debt including letters of credit as of the reporting period date as compared to trailing twelve month consolidated total EBITDA.

No definition available.

Name:	gk_MaximumLeverageRatioRequired
Namespace Prefix:	gk_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

The required minimum interest coverage ratio is calculated as the ratio of consolidated EBITDA for the four consecutive quarters as compared to consolidated interest expense for the same period.

No definition available.

Name:	gk_RequiredMinimumInterestCoverageRatio
Namespace Prefix:	gk_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

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.

No definition available.