Supplemental Balance Sheets and Statements of Operations Detail Supplemental Balance Sheets and Statements of Operations - Inventory and Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Inventory [Line Items]
Raw materials and supplies	$ 93,464	$ 97,119
Work in process	85,122	71,374
Finished goods	82,311	88,175
Inventory gross	260,897	256,668
Inventory reserves	(17,687)	(15,539)
Inventory, net	243,210	241,129
Inventory Valuation Reserve
Inventory [Line Items]
Balance at the beginning of the period	15,539	16,346	$ 15,941
Charge (benefit) to costs and expenses	12,623	6,019	4,994
Deductions	(10,867)	(6,826)	(6,954)
Other	392	0	2,365
Balance at the end of the period	17,687	$ 15,539	$ 16,346
Inventory Valuation Reserve | TOKIN
Inventory [Line Items]
Balance at the end of the period	$ 1,900