Impairment charges (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Write down of long-lived assets	$ 0	$ 6,200	$ 0	$ 6,193	$ 0
Film and Electrolytic
Property, Plant and Equipment [Line Items]
Write down 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 of long-lived assets		$ 2,100
Solid Capacitors | Facility Closing [Member]
Property, Plant and Equipment [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	100			100
Restructuring and related cost, expected cost remaining	$ 1,100			$ 1,100