Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 21,730		$ 21,730		$ 16,953
Intangible Assets, Gross (Excluding Goodwill)	84,102		84,102		46,734
Indefinite-Lived Trademarks	15,029		15,029		7,207
Goodwill	40,294		40,294		40,294
Amortization of Intangible Assets	1,400	$ 600	2,300	$ 1,100
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	5,800		5,800
Corporate, Non-Segment [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	4,710		4,710		4,710
Goodwill acquired during the year	0
Impairment charges	0
Solid Capacitors [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	35,584		35,584		35,584
Goodwill acquired during the year	0
Impairment charges	0
Film and Electrolytic [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	0		0		0
Goodwill acquired during the year	0
Impairment charges	0
Electro-magnetic, Sensors & Actuators [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	0		0
Purchased technology, customer relationships and patents (2 - 21 years)
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	69,073		69,073		39,527
Finite-Lived Intangible Assets, Accumulated Amortization	$ 21,730		$ 21,730		$ 16,953
Purchased technology, customer relationships and patents (2 - 21 years) | Weighted Average [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	14 years	16 years 8 months