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

Revenue Recognition - Net Sales Disaggregated by Product Line and Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Net sales	$ 23,082	$ 25,286	$ 21,643	$ 20,593	$ 23,641	$ 17,198	$ 21,441	$ 29,551	$ 90,604	$ 91,831	$ 77,534
Asia [Member]
Disaggregation Of Revenue [Line Items]
Net sales									5,517	10,292	10,200
Canada [Member]
Disaggregation Of Revenue [Line Items]
Net sales									8,907	16,602	8,888
Middle East [Member]
Disaggregation Of Revenue [Line Items]
Net sales									13,112	2,610	3,785
South America [Member]
Disaggregation Of Revenue [Line Items]
Net sales									3,783	324	1,560
U.S. [Member]
Disaggregation Of Revenue [Line Items]
Net sales									58,042	59,441	51,950
All Other [Member]
Disaggregation Of Revenue [Line Items]
Net sales									1,243	2,562	1,151
Heat Transfer Equipment [Member]
Disaggregation Of Revenue [Line Items]
Net sales									31,986	24,785	27,023
Vacuum Equipment [Member]
Disaggregation Of Revenue [Line Items]
Net sales									33,354	34,461	22,175
All Other [Member]
Disaggregation Of Revenue [Line Items]
Net sales									$ 25,264	$ 32,585	$ 28,336