Concentrations of Risks (Details) $ in Thousands, € in Millions, ¥ in Millions, R$ in Millions, $ in Millions, $ in Millions, ₩ in Billions																3 Months Ended		6 Months Ended
	Sep. 16, 2018 USD ($)	Sep. 16, 2018 KRW (₩)	Jun. 27, 2018 USD ($)	Jun. 27, 2018 CAD ($)	Mar. 21, 2018 EUR (€)	Mar. 21, 2018 USD ($)	Jul. 26, 2016 USD ($)	Jul. 26, 2016 BRL (R$)	May 02, 2016 USD ($) installment suit	Mar. 29, 2016 USD ($)	Mar. 29, 2016 JPY (¥)	Dec. 09, 2015 USD ($)	Dec. 09, 2015 TWD ($)	Sep. 02, 2015 USD ($) installment	Jul. 31, 2013 defendant suit	Sep. 30, 2018 USD ($)	Sep. 30, 2017	Sep. 30, 2018 USD ($)	Sep. 30, 2017	Mar. 31, 2018 USD ($)
Concentration of Risk
Accounts Payable, Trade, Current																$ 138,253		$ 138,253		$ 139,989
Accrued expenses (1)																96,666		96,666		125,119
Other non-current obligations (1)																$ 128,427		$ 128,427		$ 152,249
Revenue from Contract with Customer [Member] | Sales risk
Concentration of Risk
Concentration Risk, Customer																1
Revenue from Contract with Customer [Member] | Sales risk | Minimum [Member]
Concentration of Risk
Concentration risk, percentage																10.00%
Revenue from Contract with Customer [Member] | Electronics distributor risk
Concentration of Risk
Concentration risk, percentage																		41.50%	38.60%
Accounts receivable | Sales risk
Concentration of Risk
Concentration Risk, Customer																0	0	0	0
Accounts receivable | Credit Concentration Risk [Member]
Concentration of Risk
Concentration Risk, Customer																			0
Accounts receivable | Credit Concentration Risk [Member] | Maximum
Concentration of Risk
Concentration risk, percentage																		10.00%
Sales Revenue, Goods, Net [Member] | Sales risk
Concentration of Risk
Concentration Risk, Customer																1	1	1	1
Sales Revenue, Goods, Net [Member] | Sales risk | Minimum [Member]
Concentration of Risk
Concentration risk, percentage																10.00%	10.00%	10.00%	10.00%
Sales Revenue, Goods, Net [Member] | Electronics distributor risk
Concentration of Risk
Concentration risk, percentage																41.40%	35.60%
Indemnification Agreement [Member] | Equity Method Investments [Member]
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party														$ 13,800
Settled Litigation [Member] | Indemnification Agreement [Member] | Equity Method Investments [Member]
Concentration of Risk
Litigation Settlement, Payment Period														5 years
Litigation Settlement, Number of Payment Installments | installment														6
Litigation Settlement, Amount Awarded to Other Party														$ 2,300
Japan, Yen | JAPAN
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party | ¥											¥ 127.2
Taiwan, New Dollars | TAIWAN, PROVINCE OF CHINA
Concentration of Risk
Loss Contingency, Damages Sought, Value													$ 1,200.0
Taiwan, New Dollars | TAIWAN, PROVINCE OF CHINA | Minimum [Member]
Concentration of Risk
Loss Contingency, Damages Sought, Value													$ 609.1
United States of America, Dollars | TAIWAN, PROVINCE OF CHINA
Concentration of Risk
Loss Contingency, Damages Sought, Value												$ 39,900
United States of America, Dollars | TAIWAN, PROVINCE OF CHINA | Minimum [Member]
Concentration of Risk
Loss Contingency, Damages Sought, Value												$ 19,900
United States of America, Dollars | JAPAN
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party										$ 1,100
United States of America, Dollars | BRAZIL | Settled Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value							$ 200
Brazil, Brazil Real | BRAZIL | Settled Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value | R$								R$ 0.6
TOKIN [Member]
Concentration of Risk
Loss Contingency Accrual																$ 51,800		$ 51,800
TOKIN [Member] | United States of America, Dollars | CANADA | Settled Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value			$ 2,200
TOKIN [Member] | Canada, Dollars | CANADA | Settled Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value				$ 2.9
NEC TOKIN Corporation [Member] | Indemnification Agreement [Member] | Equity Method Investments [Member]
Concentration of Risk
Litigation Settlement, Number of Payment Installments | installment									5
Litigation Settlement, Amount Awarded to Other Party									$ 37,300
NEC TOKIN Corporation [Member] | Preliminary Settlement [Member] | Indemnification Agreement [Member] | Equity Method Investments [Member]
Concentration of Risk
Loss Contingency, Pending Claims, Number | suit									2
Unfavorable Regulatory Action [Member]
Concentration of Risk
Accounts Payable, Trade, Current																10,000		10,000
Accrued expenses (1)																19,200		19,200
Other non-current obligations (1)																22,600		$ 22,600
Lithium Ion Batteries Antitrust Litigation [Member]
Concentration of Risk
Loss Contingency, Number of Defendants | defendant															8
Loss Contingency, Pending Claims, Number | suit															2
Lithium Ion Batteries Antitrust Litigation [Member] | TOKIN [Member]
Concentration of Risk
Loss Contingency, Number of Defendants | defendant															1
Battery Action Class Suit - Indirect Product Purchasers [Member]
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party																2,000
Battery Action Class Suit [Member]
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party																$ 4,950
Competition Laws of the European Union [Member] | TOKIN [Member] | United States of America, Dollars
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party						$ 10,300
Competition Laws of the European Union [Member] | TOKIN [Member] | Euro Member Countries, Euro
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party | €					€ 8.8
Competition Laws of the European Union [Member] | NEC TOKIN Corporation [Member] | United States of America, Dollars
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party						$ 5,900
Competition Laws of the European Union [Member] | NEC TOKIN Corporation [Member] | Euro Member Countries, Euro
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party | €					€ 5.0
Monopoly and Fair Trade Laws [Member] | TOKIN [Member] | United States of America, Dollars | KOREA, REPUBLIC OF
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party	$ 7,300
Monopoly and Fair Trade Laws [Member] | TOKIN [Member] | Korea (South), Won | KOREA, REPUBLIC OF
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party | ₩		₩ 8.2