Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Statement of Cash Flows [Abstract]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 207,918	$ 286,846	$ 109,774
Restricted Cash	0	0	0
Operating activities:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	206,587	254,127	47,157
Adjustments to reconcile net income to net cash provided by (used in) operating activities, net of effect of acquisitions:
Depreciation and amortization (1)	52,628	50,661	38,151
Stock-based compensation expense	3,304	(76,192)	(41,643)
Business combination bargain purchase, gain recognized	0	(130,880)	0
Non-cash debt and financing costs	1,872	2,467	761
Loss on early extinguishment of debt	15,946	486	0
Change in value of TOKIN options	0	0	(10,700)
Net (gain) loss on sales and disposals of assets	700	(1,200)	400
Stock-based compensation expense	12,866	7,657	4,720
Pension and other post-retirement benefits	4,938	4,717	2,543
Change in deferred income taxes (1)	(49,757)	564	(15)
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down	1,660	(992)	10,671
Rent receivable	0	2,645	0
Other, net (1)	(285)	(680)	(392)
Changes in assets and liabilities, net of the effect of acquisitions:
Accounts receivable (1)	(8,910)	30,217	(2,630)
Inventories	(42,806)	(13,827)	16,805
Prepaid expenses and other assets	(4,381)	4,330	(1,769)
Accounts payable	7,650	(16,053)	6,170
Accrued income taxes	1,046	1,317	144
Other operating liabilities (1)	(70,627)	197	1,694
Net cash provided by (used in) operating activities	131,731	120,761	71,667
Investing activities:
Capital expenditures	(146,056)	(65,004)	(25,617)
Contributions to equity method investments	(4,000)	(3,000)	0
Proceeds from dividend	776	2,745	0
Acquisitions, net of cash received	0	(163,985)	0
Proceeds from sale of discontinued operations		3,400
Proceeds from sale of assets	2,268	3,638	19
Net cash provided by (used in) investing activities	(147,012)	102,364	(25,598)
Financing activities:
Proceeds from revolving line of credit	0	0	12,000
Payments of revolving line of credit	0	(33,881)	(12,000)
Proceeds from issuance of debt	298,336	334,978	2,314
Payment of long-term debt	(344,461)	(365,938)	(2,428)
Payment for Debt Extinguishment or Debt Prepayment Cost	(3,234)	0	0
Debt issuance costs	(2,021)	(5,002)	0
Proceeds from exercise of stock options	485	5,207	1,133
Proceeds from exercise of stock warrants	0	8,838	0
Purchase of treasury stock	0	0	(1,144)
Payments of Ordinary Dividends, Common Stock	(5,762)	0	0
Net cash provided by (used in) financing activities	(56,657)	(55,798)	(125)
Net increase (decrease) in cash, cash equivalents, and restricted cash	(71,938)	167,327	45,944
Effect of foreign currency fluctuations on cash (2)	(6,990)	9,745	(1,174)
Cash, cash equivalents, and restricted cash at end of fiscal year	207,918	286,846	109,774
Supplemental Cash Flow Statement Information:
Interest paid, net of capitalized interest	11,965	44,905	38,922
Income taxes paid	$ 10,863	$ 7,120	$ 4,153