Pension Plan (Narrative) (Details) (USD $)	6 Months Ended
Jun. 30, 2013
Pension Plan [Abstract]
Approximate contribution to the plan for 2013	$ 1,315,301

Amount of employer's best estimate of contributions expected to be paid to the plan in the current remaining fiscal period.

No definition available.

Name:	gni_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
Namespace Prefix:	gni_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration