Acquisitions Acquisitions - Bargain Purchase Gain (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Apr. 19, 2017	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2017
Business Acquisition [Line Items]
Less: fair value of net assets acquired	$ (416,629)
Bargain purchase gain			$ (130,880)	$ 0	$ 0
Exchange rate	10900.70%	11257.40%		11182.30%		11250.20%
TOKIN
Business Acquisition [Line Items]
Bargain purchase gain	$ (62,159)	$ (60,300)
TOKIN
Business Acquisition [Line Items]
Net consideration transferred	150,358
NEC TOKIN Corporation | Stock Purchase Agreement | KEMET Electronics Corporation
Business Acquisition [Line Items]
Preliminary fair value of KEMET’s previously held equity interest in TOKIN	204,112
Japan, Yen | TOKIN
Business Acquisition [Line Items]
Amount of debt TOKIN owed NEC	25,400,000
United States of America, Dollars | TOKIN
Business Acquisition [Line Items]
Amount of debt TOKIN owed NEC	$ 233,200