Restructuring Charges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Restructuring Charges
Restructuring charges (credits)	$ 3,530	$ (369)	$ 6,536	$ 4,317
Reconciliation of restructuring liability
Costs charged to expense	3,530	(369)	6,536	4,317
Film and Electrolytic [Member]
Restructuring Charges
Headcount reduction	2,200		2,200
TOKIN [Member]
Restructuring Charges
Headcount reduction	100		100
Employee Severance
Restructuring Charges
Opening Balance Sheet			0	0
Restructuring charges (credits)	3,278	(215)	4,389	1,864
Reconciliation of restructuring liability
Beginning of period	1,494	2,101	999	976
Costs charged to expense	3,278	(215)	4,389	1,864
Costs paid or settled	(444)	(579)	(1,080)	(1,510)
Change in foreign exchange	49	(46)	69	(69)
End of period	4,377	1,261	4,377	1,261
Employee Severance | Corporate, Non-Segment [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	957
Restructuring and Related Cost, Cost Incurred to Date	2,134		2,134
Restructuring and Related Cost, Expected Cost	3,127		3,127
Employee Severance | 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	897		897
Employee Severance | Film and Electrolytic [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	2,202
Restructuring and Related Cost, Cost Incurred to Date	2,202		2,202
Restructuring and Related Cost, Expected Cost	5,000		5,000
Employee Severance | TOKIN [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	143
Restructuring and Related Cost, Cost Incurred to Date	143		143
Restructuring and Related Cost, Expected Cost	5,328		5,328
Employee Severance | FLORIDA
Restructuring Charges
Restructuring charges (credits)	1,000		2,100	300
Reconciliation of restructuring liability
Costs charged to expense	1,000		2,100	300
Employee Severance | UNITED KINGDOM
Restructuring Charges
Restructuring charges (credits)				200
Reconciliation of restructuring liability
Costs charged to expense				200
Employee Severance | Tennessee
Restructuring Charges
Restructuring charges (credits)				400
Reconciliation of restructuring liability
Costs charged to expense				400
Employee Severance | Mexico | K-Salt
Restructuring Charges
Restructuring charges (credits)				100
Reconciliation of restructuring liability
Costs charged to expense				100
Employee Severance | Europe
Restructuring Charges
Restructuring charges (credits)				300
Reconciliation of restructuring liability
Costs charged to expense				300
Employee Severance | SWEDEN
Restructuring Charges
Restructuring charges (credits)				300
Reconciliation of restructuring liability
Costs charged to expense				300
Employee Severance | Matamoros Mexico [Member] | Solid Capacitors
Restructuring Charges
Restructuring charges (credits)				300
Reconciliation of restructuring liability
Costs charged to expense				300
Facility Closing [Member] | Corporate, Non-Segment [Member]
Restructuring Charges
Restructuring and Related Cost, Incurred Cost	0
Restructuring and Related Cost, Cost Incurred to Date	909		909
Restructuring and Related Cost, Expected Cost	909		909
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	2,098		2,098
Facility Closing [Member] | Film and Electrolytic [Member]
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
Facility Closing [Member] | TOKIN [Member]
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
Manufacturing Relocation
Restructuring Charges
Opening Balance Sheet			314	0
Restructuring charges (credits)	252	(154)	2,147	2,453
Reconciliation of restructuring liability
Beginning of period	312	1,982	406	0
Costs charged to expense	252	(154)	2,147	2,453
Costs paid or settled	(252)	(832)	(2,553)	(1,457)
Change in foreign exchange	(1)	0	(3)	0
End of period	311	996	311	996
Manufacturing Relocation | Film and Electrolytic [Member]
Restructuring Charges
Restructuring charges (credits)		100		400
Reconciliation of restructuring liability
Costs charged to expense		100		400
Manufacturing Relocation | FLORIDA
Restructuring Charges
Restructuring charges (credits)			900
Reconciliation of restructuring liability
Costs charged to expense			900
Manufacturing Relocation | Tennessee
Restructuring Charges
Restructuring charges (credits)		300		1,900
Restructuring accrual adjustment	100
Reconciliation of restructuring liability
Costs charged to expense		300		1,900
Manufacturing Relocation | SOUTH CAROLINA
Restructuring Charges
Restructuring charges (credits)		100		100
Reconciliation of restructuring liability
Costs charged to expense		$ 100		100
Manufacturing Relocation | Mexico | K-Salt
Restructuring Charges
Restructuring charges (credits)				100
Reconciliation of restructuring liability
Costs charged to expense				$ 100
Manufacturing Relocation | Victoria Mexico [Member] | Solid Capacitors
Restructuring Charges
Restructuring accrual adjustment			100
Manufacturing Relocation | Matamoros Mexico [Member] | K-Salt
Restructuring Charges
Restructuring charges (credits)	100		800
Reconciliation of restructuring liability
Costs charged to expense	$ 100		800
Employee Relocation [Member] | Tennessee
Restructuring Charges
Restructuring charges (credits)			400
Reconciliation of restructuring liability
Costs charged to expense			$ 400