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

Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Schedule Of Intangible Assets [Line Items]
Intangibles not subject to amortization, Gross Carrying Amount	$ 12,800		$ 12,800	$ 12,800
Intangibles not subject to amortization, Impairment Loss			12,800	9,100
Intangibles not subject to amortization, Net Carrying Amount	0		0	3,700
Permits [Member]
Schedule Of Intangible Assets [Line Items]
Intangibles not subject to amortization, Gross Carrying Amount	10,300		10,300	10,300
Intangibles not subject to amortization, Impairment Loss	1,700	$ 8,600	10,300	8,600
Intangibles not subject to amortization, Net Carrying Amount				1,700
Tradename [Member]
Schedule Of Intangible Assets [Line Items]
Intangibles not subject to amortization, Gross Carrying Amount	2,500		2,500	2,500
Intangibles not subject to amortization, Impairment Loss	2,000	$ 500	2,500	500
Intangibles not subject to amortization, Net Carrying Amount				2,000
Customer Relationships [Member]
Schedule Of Intangible Assets [Line Items]
Intangibles subject to amortization, Gross Carrying Amount	2,700		2,700	2,700
Intangibles subject to amortization, Accumulated Amortization	1,492		1,492	1,312
Intangibles subject to amortization, Impairment Loss			$ 1,208
Intangibles subject to amortization, Net Carrying Amount				$ 1,388
Intangibles not subject to amortization, Impairment Loss	$ 1,208