Concentrations of Risks (Details) $ in Thousands, € in Millions, ¥ in Millions, R$ in Millions, $ in Millions, $ in Millions, ₩ in Billions																	3 Months Ended
		Nov. 30, 2018 USD ($)	Nov. 30, 2018 KRW (₩)	Jun. 27, 2018 USD ($)	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 ($) installment	Jul. 31, 2013 defendant suit	Jun. 30, 2019 USD ($)	Jun. 30, 2018	Mar. 31, 2019 USD ($)
Concentration of Risk
Accounts Payable, Trade, Current																	$ 161,853		$ 153,287
Accrued Liabilities, Current	[1]																79,173		93,761
Other non-current obligations	[1]																$ 149,267		$ 125,360
Sales revenue | Sales risk
Concentration of Risk
Concentration Risk, Customer																	1	1
Sales revenue | Sales risk | Minimum [Member]
Concentration of Risk
Concentration risk, percentage																	10.00%	10.00%
Sales revenue | Electronics distributor risk
Concentration of Risk
Concentration risk, percentage																	42.90%	41.70%
Accounts receivable | Sales risk
Concentration of Risk
Concentration Risk, Customer																	0	0
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
TAIWAN, PROVINCE OF CHINA
Concentration of Risk
Loss Contingency, Damages Sought, Value													$ 39,200	$ 1,200.0
TAIWAN, PROVINCE OF CHINA | Minimum [Member]
Concentration of Risk
Loss Contingency, Damages Sought, Value													$ 19,600	$ 609.1
JAPAN
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party											$ 1,100	¥ 127.2
BRAZIL | Settled Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value								$ 200	R$ 0.6
TOKIN [Member]
Concentration of Risk
Loss Contingency Accrual																	$ 26,300
TOKIN [Member] | CANADA | Settled Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value				$ 2,200	$ 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
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]
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party						€ 8.8	$ 10,300
Competition Laws of the European Union [Member] | NEC TOKIN Corporation [Member]
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party						€ 5.0	$ 5,900
Monopoly and Fair Trade Laws [Member] | TOKIN [Member] | KOREA, REPUBLIC OF
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party		$ 7,200	₩ 8.1
AASI and Benchmark Complaints [Member] | TOKIN [Member]
Concentration of Risk
Litigation Settlement, Amount Awarded to Other Party																	950
Accounts Payable [Member] | Unfavorable Regulatory Action [Member] | TOKIN [Member]
Concentration of Risk
Accounts Payable, Trade, Current																	7,300
Accrued Liabilities [Member] | Unfavorable Regulatory Action [Member] | TOKIN [Member]
Concentration of Risk
Accrued Liabilities, Current																	6,900
Other Noncurrent Liabilities [Member] | Unfavorable Regulatory Action [Member] | TOKIN [Member]
Concentration of Risk
Other non-current obligations																	12,100
Taiwan, New Dollars | TOKIN [Member] | TAIWAN, PROVINCE OF CHINA | Pending Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value																	182,700
United States of America, Dollars | TOKIN [Member] | TAIWAN, PROVINCE OF CHINA | Pending Litigation [Member]
Concentration of Risk
Loss Contingency, Damages Paid, Value																	$ 5,900

[1]   June 30, 2019   March 31, 2019 ASSETS  
   
Current assets:  
   
Cash and cash equivalents $ 217,307
  $ 207,918
Accounts receivable, net 154,522
  154,059
Inventories, net 256,140
  241,129
Prepaid expenses and other current assets 48,187
  38,947
Total current assets 676,156
  642,053
Property, plant and equipment, net of accumulated depreciation of $889,142 and $880,451 as of June 30, 2019 and March 31, 2019, respectively 518,310
  495,280
Goodwill 40,294
  40,294
Intangible assets, net 53,448
  53,749
Equity method investments 14,238
  12,925
Deferred income taxes  44,544
  57,024
Other assets 44,216
  16,770
Total assets $ 1,391,206
  $ 1,318,095
        LIABILITIES AND STOCKHOLDERS’ EQUITY  
   
Current liabilities:  
   
Current portion of long-term debt $ 29,225
  $ 28,430
Accounts payable 161,853
  153,287
Accrued expenses 79,173
  93,761
Income taxes payable 808
  2,995
Total current liabilities  271,059
  278,473
Long-term debt 282,871
  266,041
Other non-current obligations 149,267
  125,360
Deferred income taxes  11,214
  8,806
Total liabilities 714,411
  678,680
Stockholders’ equity:  
   
Preferred stock, par value $0.01, authorized 10,000 shares, none issued —
  —
Common stock, par value $0.01, authorized 175,000 shares, issued 58,018 and 57,822 shares at June 30, 2019 and March 31, 2019, respectively 580
  578
Additional paid-in capital 466,704
  465,366
Retained earnings 241,635
  204,195
Accumulated other comprehensive income (loss) (32,124 )   (30,724 ) Total stockholders’ equity 676,795
  639,415
Total liabilities and stockholders’ equity $ 1,391,206
  $ 1,318,095