Arrangements with Off-Balance Sheet Risk - Narrative (Details) - May. 31, 2015 - USD ($)	Total
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Outstanding surety bonds	$ 43,300,000
Guarantee obligations	$ 120,000,000.0
Standard warranty period	1 year
Rocketdyne Business [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Amount related to the pending future acquisition of UTC's ownership	$ 55,000,000
Expected future acquisition of ownership interest percentage	50.00%
Senior Credit Facility [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Outstanding commercial letters of credit	$ 46,400,000

Product Warranty, Period

No definition available.

Name:	gy_ProductWarrantyPeriod
Namespace Prefix:	gy_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Surety Bond Outstanding

+ References

No definition available.

+ Details

Name:	gy_SuretyBondOutstanding
Namespace Prefix:	gy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (g)(1)

-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of voting equity interests acquired in a business combination achieved in stages, including equity interests in the acquiree held by the acquirer immediately before the acquisition date and acquired at the acquisition date.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeIncludingSubsequentAcquisitionPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_BusinessAcquisitionAxis=gy_RocketdyneBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=gy_SeniorCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: