Supplemental Balance Sheets and Statements of Operations Detail Supplemental Balance Sheets and Statements of Operations - Inventory and Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Inventory [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 88,408	$ 65,750
Inventory, Work in Process, Gross	65,417	47,408
Inventory, Finished Goods, Gross	66,907	50,738
Inventory, Gross	220,732	163,896
Inventory Valuation Reserves	16,346	15,941
Inventory, Net	204,386	147,955
Inventory Valuation Reserve
Inventory [Line Items]
Balance at the beginning of the period	15,941	16,101	$ 17,499
Charged to Cost and Expense	4,994	6,163	5,696
Deductions	6,954	6,125	7,326
Other	2,365	(198)	232
Balance at the end of the period	16,346	$ 15,941	$ 16,101
Inventory Valuation Reserve \| TOKIN
Inventory [Line Items]
Balance at the end of the period	$ 1,900

Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer.

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Gross amount, as of the balance sheet date, of merchandise, goods, commodities, or supplies held for future sale or to be used in manufacturing, servicing or production process.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

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Amount of valuation reserve for inventory.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
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Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer.

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Amount of increase (decrease) in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from adjustments.

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Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

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Amount of increase in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from charges to costs and expenses.

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Total of the deductions in a given period to allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, representing receivables written off as uncollectible and portions of the reserves utilized, respectively.

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