XML 24 R30.htm IDEA: XBRL DOCUMENT v3.3.0.814

Investments - Additional Information (Detail)	6 Months Ended
	Sep. 30, 2015
Minimum [Member]
Investment Securities [Line Items]
Treasury with original maturities period	3 months
Maximum [Member]
Investment Securities [Line Items]
Investment maturity date range end	Aug. 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

Investment Securities [Line Items]

+ References

No definition available.

+ Details

Name:	ghm_InvestmentSecuritiesLineItems
Namespace Prefix:	ghm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The maturity date of the investment.

+ References

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



-Publisher SEC



-Name Regulation S-X (SX)



-Number 210



-Article 12



-Section 12



-Sentence Column A

+ Details

Name:	invest_InvestmentMaturityDate1
Namespace Prefix:	invest_
Data Type:	xbrli:dateItemType
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: