Restructuring - Narrative (Details) $ in Thousands	12 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($) employee
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 14,843	$ 5,404	$ 4,178
Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	12,587	2,214	$ 1,803
Expected number of positions eliminated | employee			50
Number of positions eliminated from inception to date | employee			24
Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,256	3,190	$ 2,375
Employee Relocation
Restructuring Cost and Reserve [Line Items]
Restructuring charges	200
Solid Capacitors
Restructuring Cost and Reserve [Line Items]
Restructuring charges	983	1,333	1,916
Solid Capacitors | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Cumulative incurred to date	0
Solid Capacitors | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative incurred to date	0
Film and Electrolytic
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5,788	3,738	1,714
Workforce reductions and administrative overhead	5,200
Film and Electrolytic | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Cumulative incurred to date	5,243
Film and Electrolytic | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		600
Film and Electrolytic | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative incurred to date	0
TOKIN | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	4,400
Mexico | Solid Capacitors | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		300	900
Mexico | Solid Capacitors | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative incurred to date		600
Mexico | K-Salt [Member] | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		100
China | Film and Electrolytic | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			600
China | Film and Electrolytic | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			400
Europe North America and Asia [Domain] | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			500
Matamoros Mexico [Member] | K-Salt [Member] | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	800
TENNESSEE | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		400
TENNESSEE | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		1,900
TENNESSEE | Employee Relocation
Restructuring Cost and Reserve [Line Items]
Restructuring charges	400
Victoria Mexico [Member] | Solid Capacitors | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			500
Victoria Mexico [Member] | Solid Capacitors | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			400
Accrual adjustment	100	100
Europe and North America [Member] | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			500
Europe
Restructuring Cost and Reserve [Line Items]
Workforce reductions and administrative overhead	200
Europe | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		300
Europe | Film and Electrolytic | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			300
Sweden | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		300
FLORIDA | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2,700	300
FLORIDA | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 900
SOUTH CAROLINA | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		300
United Kingdom | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 200
Italy | Film and Electrolytic | Personnel Reduction Costs
Restructuring Cost and Reserve [Line Items]
Accrual adjustment			(1,000)
Landsberg Germany [Member] | Film and Electrolytic | Manufacturing and sales office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 1,100
Customer Relationships
Restructuring Cost and Reserve [Line Items]
Useful life	12 years 3 months 12 days	15 years 8 months 6 days