XML 54 R43.htm IDEA: XBRL DOCUMENT v3.21.2

Investments - Additional Information (Detail)	3 Months Ended
	Jun. 30, 2021 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Investments	$ 0
Minimum [Member]
Schedule of Held-to-maturity Securities [Line Items]
Treasury with original maturities period	3 months
Maximum
Schedule of Held-to-maturity Securities [Line Items]
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

Sum of the carrying amounts as of the balance sheet date of all investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(h))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_Investments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: