Income Taxes Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	$ 7,500,000	$ 7,000,000	$ 3,300,000
Change in U.S. valuation allowance	(66,948,000)	(7,080,000)	4,099,000
Expired foreign tax credits	$ 407,000	4,766,000	0
Deferred tax assets period of cumulative loss for determination of full valuation allowance	3 years
Deferred tax liabilities, unremitted foreign earnings	$ 0
Unrecognized tax benefits	8,680,000	7,390,000	$ 7,103,000	$ 6,377,000
Unrecognized tax benefits that would impact effective tax rate	4,300,000
Amount of unrecorded benefit	3,300,000
Income tax penalties and interest accrued	900,000	$ 200,000
Tax Cuts & Jobs Act	800,000
Tax repatriation charge	$ 79,300,000
Macedonia
Operating Loss Carryforwards [Line Items]
Statutory tax rate, percent	0.00%	10.00%	10.00%
Thailand
Operating Loss Carryforwards [Line Items]
Statutory tax rate, percent	0.00%	20.00%
Valuation Allowance for Deferred Tax Assets
Operating Loss Carryforwards [Line Items]
Valuation allowances and reserves	$ 171,401,000	$ 163,898,000	$ 170,917,000	$ 167,594,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	74,400,000
Operating loss carryforwards	157,700,000
Operating loss carryforwards subject to expiration within one year	300,000
Foreign Tax Authority | TOKIN
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	78,200,000
Foreign Tax Authority | Other Foreign Operations
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	(3,800,000)
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	$ 1,200,000
Other information pertaining to income taxes	51.3
Operating loss carryforwards	$ 240,000,000
Domestic Tax Authority | TOKIN
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	(21,100,000)
Domestic Tax Authority | Deferred Tax Assets under U.S. Tax Reform
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	(49,400,000)
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	530,400,000
Operating loss carryforwards subject to expiration within one year	$ 5,100,000
Operating loss carryforwards, expiration period	1 year
Macedonia
Operating Loss Carryforwards [Line Items]
Income tax holiday, aggregate dollar amount	$ 0