Graham Corporation Quarterly report pursuant to Section 13 or 15(d)

Income Taxes - Additional Information (Detail) - USD ($)	6 Months Ended
	Sep. 30, 2019	Mar. 31, 2019
Income Taxes [Line Items]
Liability unrecognized tax benefits	$ 0	$ 0
Earliest Tax Year [Member] \| Federal Tax Jurisdictions [Member]
Income Taxes [Line Items]
Open tax year	2015
Earliest Tax Year [Member] \| State Tax Jurisdictions [Member]
Income Taxes [Line Items]
Open tax year	2014
Earliest Tax Year [Member] \| International Tax Jurisdictions [Member]
Income Taxes [Line Items]
Open tax year	2016
Latest Tax Year [Member] \| Federal Tax Jurisdictions [Member]
Income Taxes [Line Items]
Open tax year	2018
Latest Tax Year [Member] \| State Tax Jurisdictions [Member]
Income Taxes [Line Items]
Open tax year	2018
Latest Tax Year [Member] \| International Tax Jurisdictions [Member]
Income Taxes [Line Items]
Open tax year	2018