XML 84 R89.htm IDEA: XBRL DOCUMENT
v3.20.1

Quarterly Financial Data (Unaudited) - Summary of Company's Unaudited Quarterly Results (Parenthetical) (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Mar. 31, 2019 | Mar. 31, 2018
Loss from impairment of goodwill and intangible assets | $ 6,449 | $ 6,449 | $ 14,816
Income tax benefit on goodwill and intangible assets impairment | 1,129 |  |
Commercial Nuclear Utility Business [Member] |  |  |
Loss from impairment of goodwill and intangible assets | $ 6,449 |  |

X
- Definition Amount of income tax benefit pertaining to the loss recognized during the period from the impairment of goodwill and the impairment of the carrying amount of tangible and intangible assets, other than goodwill. + References No definition available. + Details
Name: | ghm_IncomeTaxBenefitOnAssetImpairmentCharges
Namespace Prefix: | ghm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228 + Details
Name: | us-gaap_AssetImpairmentCharges
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_SubsegmentsAxis=ghm_CommercialNuclearUtilityBusinessMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |