Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020
Inventory [Line Items]
Raw materials	$ 89,168	$ 85,452
Work-in-process	22,223	25,876
Finished goods	33,350	33,216
At cost - FIFO basis:	144,741	144,544
LIFO cost less than FIFO cost	(20,169)	(17,171)
Net inventories	$ 124,572	$ 127,373