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

Accounting and Repoting Changes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of net benefit income	$ 206	$ 120	$ 412	$ 239
ASU 2017-07 [Member] \| Selling, General and Administrative Expense [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of net benefit income		$ 31		$ 62
Reclassification of net benefit income [Extensible List]		us-gaap:OtherIncomeMember		us-gaap:OtherIncomeMember
ASU 2017-07 [Member] \| Cost of Products Sold [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of net benefit income		$ 89		$ 177
Reclassification of net benefit income [Extensible List]		us-gaap:OtherIncomeMember		us-gaap:OtherIncomeMember