(Gain) Loss on Write-Down and Disposal of Long-Lived Assets Impairment Charges - Narrative (Details) - USD ($)	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		$ 1,200,000
Proceeds from sale of discontinued operations		3,400,000
Gain (Loss) on Sale of Properties		1,900,000
Cost of Real Estate Sales		200,000
Property, Plant and Equipment, Disposals			$ 400,000
Write down of long-lived assets				$ 0
Asset Impairment Charges		200,000	10,279,000
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		(992,000)	10,671,000	375,000
Solid Capacitors
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		(600,000)
Asset Impairment Charges	$ 10,300,000		2,100,000
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		689,000	2,303,000	536,000
Film and Electrolytic
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		(3,600,000)
Asset Impairment Charges			8,200,000
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		(3,356,000)	8,339,000	(270,000)
KFM [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		(1,400,000)
Electro-magnetic, Sensors & Actuators [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		(1,300,000)
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		1,272,000	0	$ 0
TENNESSEE | Film and Electrolytic
Property, Plant and Equipment [Line Items]
Asset Impairment Charges			4,100,000
Impairment of Long-Lived Assets to be Disposed of			3,000,000
Impairment of Intangible Assets (Excluding Goodwill)			1,100,000
Italy | Film and Electrolytic
Property, Plant and Equipment [Line Items]
Asset Impairment Charges			4,100,000
Facility Closing [Member] | Solid Capacitors
Property, Plant and Equipment [Line Items]
Cumulative incurred to date		0
Facility Closing [Member] | Film and Electrolytic
Property, Plant and Equipment [Line Items]
Cumulative incurred to date		$ 0
Facility Closing [Member] | Mexico | Solid Capacitors
Property, Plant and Equipment [Line Items]
Cumulative incurred to date			$ 600,000
Basic [Member] | Solid Capacitors
Property, Plant and Equipment [Line Items]
Impairment Effect on Earnings Per Share, Pretax			$ 0.04
Basic [Member] | Film and Electrolytic
Property, Plant and Equipment [Line Items]
Impairment Effect on Earnings Per Share, Pretax			0.18
Diluted [Member] | Solid Capacitors
Property, Plant and Equipment [Line Items]
Impairment Effect on Earnings Per Share, Pretax		$ 0.04
Diluted [Member] | Film and Electrolytic
Property, Plant and Equipment [Line Items]
Impairment Effect on Earnings Per Share, Pretax			$ 0.15