Segment and Geographic Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017 USD ($) manufacturing_site	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) manufacturing_site business_group	Sep. 30, 2016 USD ($)
Segment and geographic information
Number of business groups | business_group			3
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	$ 301,471	$ 187,308	$ 575,471	$ 372,243
Operating income (loss)	31,643	3,374	59,427	12,672
Depreciation and amortization expense	13,326	9,440	25,569	18,876
Restructuring charges	1,393	3,998	3,006	4,686
Write down of Long-lived Assets	(39)	6,277	(20)	6,368
North and South America (“Americas”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	61,668	56,781	126,331	111,882
Europe, Middle East, Africa (“EMEA”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	66,487	60,047	133,035	120,533
Japan and Korea (“JPKO”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	44,739	0	80,119	0
Asia and Pacific Rim (“APAC”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	128,577	70,480	235,986	139,828
Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	1,393	3,998	3,006	4,686
Corporate, Non-Segment [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Operating income (loss)	(34,148)	(25,135)	(61,736)	(49,691)
Depreciation and amortization expense	2,436	1,457	4,366	2,760
Corporate, Non-Segment [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	$ 873	325	$ 2,021	328
Solid Capacitors
Segment and geographic information
Number of Manufacturing Sites | manufacturing_site	10		10
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	$ 191,267	142,641	$ 373,386	284,585
Operating income (loss)	56,717	35,574	109,426	70,841
Depreciation and amortization expense	7,547	5,147	14,590	10,565
Write down of Long-lived Assets		2,100
Solid Capacitors | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	$ 416	558	$ 720	694
Film and Electrolytic [Member]
Segment and geographic information
Number of Manufacturing Sites | manufacturing_site	9		9
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	$ 47,901	44,667	$ 95,438	87,658
Operating income (loss)	1,309	(7,065)	3,614	(8,478)
Depreciation and amortization expense	2,553	2,836	5,109	5,551
Write down of Long-lived Assets		4,100
Film and Electrolytic [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	$ 104	3,115	$ 265	3,664
Electro-magnetic, Sensors & Actuators [Member]
Segment and geographic information
Number of Manufacturing Sites | manufacturing_site	4		4
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales	$ 62,303	0	$ 106,647	0
Operating income (loss)	7,765	0	8,123	0
Depreciation and amortization expense	790	0	1,504	0
Electro-magnetic, Sensors & Actuators [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	$ 0	$ 0	$ 0	$ 0