Retirement Benefits - Changes in Prepayment Credits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Nov. 30, 2013
Compensation And Retirement Disclosure [Abstract]
Beginning balance	$ 32.5
Amount used to offset minimum required contribution	(5.4)
Adjustment for investment experience	3.5
Ending balance	$ 30.6

Defined Benefit Plan Adjustment For Investment Experience

No definition available.

Name:	gy_DefinedBenefitPlanAdjustmentForInvestmentExperience
Namespace Prefix:	gy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration