Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020
Inventory [Line Items]
Raw materials	$ 80,206	$ 85,452
Work-in-process	22,761	25,876
Finished goods	28,107	33,216
At cost - FIFO basis:	131,074	144,544
LIFO cost less than FIFO cost	(18,979)	(17,171)
Net inventories	$ 112,095	$ 127,373