Graham Corporation Annual report pursuant to Section 13 and 15(d)

Intangible Assets - Summary of Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	May 31, 2014	Mar. 31, 2014
Schedule Of Intangible Assets [Line Items]
Indefinite Lived Intangible Assets, Gross Carrying Amount	$ 12,800	$ 12,800
Indefinite Lived Intangible Assets, Accumulated Amortization	0	0
Indefinite Lived Intangible Assets, Net Carrying Amount	12,800	12,800
Permits [Member]
Schedule Of Intangible Assets [Line Items]
Indefinite Lived Intangible Assets, Gross Carrying Amount	10,300	10,300
Indefinite Lived Intangible Assets, Accumulated Amortization	0	0
Indefinite Lived Intangible Assets, Net Carrying Amount	10,300	10,300
Tradename [Member]
Schedule Of Intangible Assets [Line Items]
Indefinite Lived Intangible Assets, Gross Carrying Amount	2,500	2,500
Indefinite Lived Intangible Assets, Accumulated Amortization	0	0
Indefinite Lived Intangible Assets, Net Carrying Amount	2,500	2,500
Customer Relationships [Member]
Schedule Of Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross Carrying Amount	2,700		2,700
Finite-Lived Intangible Assets, Accumulated Amortization	772		592
Finite-Lived Intangible Assets, Net Carrying Amount	$ 1,928		$ 2,108