Segment and Geographic Information (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) manufacturing_site business_group	Jun. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)
Segment and geographic information
Number of business groups | business_group	3
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	$ 327,616	$ 273,946
Operating income (loss)	35,176	27,607
Depreciation and amortization expense	13,097	12,459
Restructuring charges	(96)	1,613
Write down of Long-lived Assets			$ 0
North and South America (“Americas”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	72,151	64,664
Europe, Middle East, Africa (“EMEA”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	74,648	66,493
Japan and Korea (“JPKO”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	47,858	35,380
Asia and Pacific Rim (“APAC”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	132,959	107,409
Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	(96)	1,613
Corporate, Non-Segment [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Operating income (loss)	(41,611)	(27,588)
Depreciation and amortization expense	1,791	1,930
Corporate, Non-Segment [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	$ (79)	1,148
Solid Capacitors
Segment and geographic information
Number of Manufacturing Sites | manufacturing_site	10
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	$ 213,821	182,119
Operating income (loss)	69,665	52,709
Depreciation and amortization expense	7,182	7,043
Solid Capacitors | North and South America (“Americas”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	63,105	58,198
Solid Capacitors | Europe, Middle East, Africa (“EMEA”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	41,466	37,632
Solid Capacitors | Japan and Korea (“JPKO”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	8,880	13,633
Solid Capacitors | Asia and Pacific Rim (“APAC”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	100,370	72,656
Solid Capacitors | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	$ (18)	304
Film and Electrolytic [Member]
Segment and geographic information
Number of Manufacturing Sites | manufacturing_site	10
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	$ 54,955	47,483
Operating income (loss)	1,067	2,128
Depreciation and amortization expense	2,620	2,772
Film and Electrolytic [Member] | North and South America (“Americas”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	6,649	4,703
Film and Electrolytic [Member] | Europe, Middle East, Africa (“EMEA”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	32,607	28,481
Film and Electrolytic [Member] | Japan and Korea (“JPKO”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	110	0
Film and Electrolytic [Member] | Asia and Pacific Rim (“APAC”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	15,589	14,299
Film and Electrolytic [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	$ 1	161
Electro-magnetic, Sensors & Actuators [Member]
Segment and geographic information
Number of Manufacturing Sites | manufacturing_site	4
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	$ 58,840	44,344
Operating income (loss)	6,055	358
Depreciation and amortization expense	1,504	714
Electro-magnetic, Sensors & Actuators [Member] | North and South America (“Americas”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	2,397	1,763
Electro-magnetic, Sensors & Actuators [Member] | Europe, Middle East, Africa (“EMEA”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	575	380
Electro-magnetic, Sensors & Actuators [Member] | Japan and Korea (“JPKO”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	38,868	21,747
Electro-magnetic, Sensors & Actuators [Member] | Asia and Pacific Rim (“APAC”)
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	17,000	20,454
Electro-magnetic, Sensors & Actuators [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	0	0
OEM [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	148,929	117,232
OEM [Member] | Solid Capacitors
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	70,388	58,991
OEM [Member] | Film and Electrolytic [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	22,441	20,441
OEM [Member] | Electro-magnetic, Sensors & Actuators [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	56,100	37,800
Distributor [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	136,686	114,749
Distributor [Member] | Solid Capacitors
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	107,634	86,920
Distributor [Member] | Film and Electrolytic [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	26,568	21,403
Distributor [Member] | Electro-magnetic, Sensors & Actuators [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	2,484	6,426
EMS [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	42,001	41,965
EMS [Member] | Solid Capacitors
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	35,799	36,208
EMS [Member] | Film and Electrolytic [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	5,946	5,639
EMS [Member] | Electro-magnetic, Sensors & Actuators [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	256	118
Tantalum [Member] | Solid Capacitors
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	134,313	116,450
Ceramics [Member] | Solid Capacitors
Segment Reporting Information, Profit (Loss) [Abstract]
Net sales (1)	$ 79,508	$ 65,669