Restructuring Charges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Charges
Restructuring charges	$ 2,920	$ 0	$ 5,128	$ (96)
Reconciliation of restructuring liability
Costs charged to expense	(2,920)	0	(5,128)	96
Employee Severance
Restructuring Charges
Restructuring charges	2,396	0	3,625	(84)
Reconciliation of restructuring liability
Beginning of period	1,789	4,170	1,865	9,629
Costs charged to expense	(2,396)	0	(3,625)	84
Costs paid or settled	(2,661)	(1,313)	(3,976)	(6,449)
Change in foreign exchange	(9)	(20)	1	(264)
End of period	1,515	2,837	1,515	2,837
Employee Severance | Film and Electrolytic [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	200
Restructuring charges			200
Reconciliation of restructuring liability
Costs charged to expense			(200)
Employee Severance | NEVADA | Solid Capacitors
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	118
Restructuring and Related Cost, Cost Incurred to Date	566		566
Restructuring and Related Cost, Expected Cost	897		897
Restructuring charges			600
Reconciliation of restructuring liability
Costs charged to expense			(600)
Employee Severance | Granna, Sweden [Member] | Film and Electrolytic [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	46
Restructuring and Related Cost, Cost Incurred to Date	719		719
Restructuring and Related Cost, Expected Cost	729		729
Restructuring charges			700
Reconciliation of restructuring liability
Costs charged to expense			(700)
Manufacturing Relocation 1 [Member]
Restructuring Charges
Restructuring charges				0
Reconciliation of restructuring liability
Costs charged to expense				0
Costs paid or settled	(523)		(1,502)
Facility Closing [Member] | NEVADA | Solid Capacitors
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	55
Restructuring and Related Cost, Cost Incurred to Date	2,860		2,860
Restructuring and Related Cost, Expected Cost	2,098		2,098
Facility Closing [Member] | Granna, Sweden [Member] | Film and Electrolytic [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	638
Restructuring and Related Cost, Cost Incurred to Date	4,242		4,242
Restructuring and Related Cost, Expected Cost	4,242		4,242
Manufacturing Relocation
Restructuring Charges
Restructuring charges	524	0	1,503	(12)
Reconciliation of restructuring liability
Beginning of period	325	317	316	330
Costs charged to expense	(524)	0	(1,503)	12
Costs paid or settled		0		0
Change in foreign exchange	(1)	(7)	8	(20)
End of period	325	$ 310	325	310
Manufacturing Relocation | NEVADA | Solid Capacitors
Restructuring Charges
Restructuring charges			(500)
Reconciliation of restructuring liability
Costs charged to expense			500
Manufacturing Relocation | Granna, Sweden [Member] | Film and Electrolytic [Member]
Restructuring Charges
Restructuring charges	600		1,900
Reconciliation of restructuring liability
Costs charged to expense	(600)		(1,900)
Employee severance 1 [Member]
Restructuring Charges
Restructuring charges				(79)
Reconciliation of restructuring liability
Costs charged to expense				$ 79
reorganization due to decline of MnO2 Products [Member] | Employee Severance | Solid Capacitors
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	1,320		1,400
Restructuring and Related Cost, Cost Incurred to Date	2,948		2,948
Restructuring and Related Cost, Expected Cost	2,948		2,948
reorganization due to decline of MnO2 Products [Member] | Facility Closing [Member] | Solid Capacitors
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	0
Restructuring and Related Cost, Cost Incurred to Date	0		0
Restructuring and Related Cost, Expected Cost	0		0
TOKIN [Member] | Employee Severance | Corporate Segment [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	$ 700		$ 700