Impairment charges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Write down and disposal of long-lived assets	$ (39)	$ 6,277	$ (20)	$ 6,368
Film and Electrolytic [Member]
Property, Plant and Equipment [Line Items]
Write down and disposal of long-lived assets		4,100
Impairment of long-lived assets to be disposed of		3,000
Impairment of Intangible assets		1,100
Solid Capacitors
Property, Plant and Equipment [Line Items]
Write down and disposal of long-lived assets		$ 2,100