XML 58 R33.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Investments - Additional Information (Detail) | 9 Months Ended
--- | ---
Dec. 31, 2015
Minimum [Member] |
Schedule of Held-to-maturity Securities [Line Items] |
Treasury with original maturities period | 3 months
Maximum [Member] |
Schedule of Held-to-maturity Securities [Line Items] |
Investment maturity date range end | Nov. 10, 2016
Treasury with original maturities period | 1 year

X
- Definition Original maturity period for held to maturity securities. + References No definition available. + Details
Name: | ghm_HeldToMaturitySecuritiesOriginalMaturityPeriod
Namespace Prefix: | ghm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Date of maturity of a debt security categorized as held-to-maturity, in CCYY-MM-DD format. + References No definition available. + Details
Name: | us-gaap_HeldtomaturitySecuritiesDebtMaturitiesDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- 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_ScheduleOfHeldToMaturitySecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |