Pension Plan (Narrative) (Details) (USD $)	3 Months Ended
Mar. 31, 2013
Pension Plan [Abstract]
Approximate contribution to the plan for 2013	$ 800,000

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