Segment and Geographic Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019 USD ($) manufacturing_site	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) business_group manufacturing_site	Sep. 30, 2018 USD ($)
Segment and geographic information
Net sales	$ 327,397	$ 349,233	$ 672,639	$ 676,849
Number of business groups | business_group			3
Segment Reporting Information, Profit (Loss) [Abstract]
Operating income (loss)	49,090	50,000	$ 107,490	85,176
Depreciation and amortization expense	15,117	12,545	29,376	25,642
Restructuring charges	2,920	0	5,128	(96)
Asia and Pacific Rim (“APAC”)
Segment and geographic information
Net sales	132,728	138,388	260,492	271,347
Europe, Middle East, Africa (“EMEA”)
Segment and geographic information
Net sales	69,663	77,732	151,369	152,380
North and South America (“Americas”)
Segment and geographic information
Net sales	79,704	82,289	173,054	154,440
Japan and Korea (“JPKO”)
Segment and geographic information
Net sales	45,302	50,824	87,724	98,682
Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	2,920	0	5,128	(96)
Corporate, Non-Segment [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Operating income (loss)	(47,649)	(46,054)	(92,714)	(87,665)
Depreciation and amortization expense	2,956	1,841	5,622	3,632
Corporate, Non-Segment [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	390	0	429	(79)
Solid Capacitors
Segment and geographic information
Net sales	$ 233,633	235,473	$ 481,840	449,294
Number of Manufacturing Sites | manufacturing_site	10		10
Segment Reporting Information, Profit (Loss) [Abstract]
Operating income (loss)	$ 93,376	84,686	$ 196,062	154,351
Depreciation and amortization expense	7,967	7,353	15,759	14,535
Solid Capacitors | Asia and Pacific Rim (“APAC”)
Segment and geographic information
Net sales	107,538	106,535	210,837	206,907
Solid Capacitors | Europe, Middle East, Africa (“EMEA”)
Segment and geographic information
Net sales	45,786	46,073	98,869	87,538
Solid Capacitors | North and South America (“Americas”)
Segment and geographic information
Net sales	69,766	73,345	152,595	136,449
Solid Capacitors | Japan and Korea (“JPKO”)
Segment and geographic information
Net sales	10,543	9,520	19,539	18,400
Solid Capacitors | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	1,493	0	1,614	(18)
Film and Electrolytic [Member]
Segment and geographic information
Net sales	$ 41,804	50,628	$ 88,513	105,583
Number of Manufacturing Sites | manufacturing_site	8		8
Segment Reporting Information, Profit (Loss) [Abstract]
Operating income (loss)	$ (1,072)	4,236	$ (3,951)	5,303
Depreciation and amortization expense	2,246	2,198	4,537	4,818
Film and Electrolytic [Member] | Asia and Pacific Rim (“APAC”)
Segment and geographic information
Net sales	11,283	12,709	22,227	28,297
Film and Electrolytic [Member] | Europe, Middle East, Africa (“EMEA”)
Segment and geographic information
Net sales	23,091	30,831	50,883	63,439
Film and Electrolytic [Member] | North and South America (“Americas”)
Segment and geographic information
Net sales	7,155	6,844	14,950	13,493
Film and Electrolytic [Member] | Japan and Korea (“JPKO”)
Segment and geographic information
Net sales	275	244	453	354
Film and Electrolytic [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	867	0	2,915	1
Electro-magnetic, Sensors & Actuators [Member]
Segment and geographic information
Net sales	$ 51,960	63,132	$ 102,286	121,972
Number of Manufacturing Sites | manufacturing_site	4		4
Segment Reporting Information, Profit (Loss) [Abstract]
Operating income (loss)	$ 4,435	7,132	$ 8,093	13,187
Depreciation and amortization expense	1,948	1,153	3,458	2,657
Electro-magnetic, Sensors & Actuators [Member] | Asia and Pacific Rim (“APAC”)
Segment and geographic information
Net sales	13,907	19,144	27,428	36,143
Electro-magnetic, Sensors & Actuators [Member] | Europe, Middle East, Africa (“EMEA”)
Segment and geographic information
Net sales	786	828	1,617	1,403
Electro-magnetic, Sensors & Actuators [Member] | North and South America (“Americas”)
Segment and geographic information
Net sales	2,783	2,100	5,509	4,498
Electro-magnetic, Sensors & Actuators [Member] | Japan and Korea (“JPKO”)
Segment and geographic information
Net sales	34,484	41,060	67,732	79,928
Electro-magnetic, Sensors & Actuators [Member] | Operating Income (Loss) [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Restructuring charges	170	0	170	0
OEM [Member]
Segment and geographic information
Net sales	145,059	154,032	288,262	302,961
OEM [Member] | Solid Capacitors
Segment and geographic information
Net sales	79,936	74,550	157,640	144,938
OEM [Member] | Film and Electrolytic [Member]
Segment and geographic information
Net sales	16,396	20,095	34,923	42,536
OEM [Member] | Electro-magnetic, Sensors & Actuators [Member]
Segment and geographic information
Net sales	48,727	59,387	95,699	115,487
Distributor [Member]
Segment and geographic information
Net sales	130,796	144,416	278,915	281,102
Distributor [Member] | Solid Capacitors
Segment and geographic information
Net sales	109,277	116,947	232,505	224,580
Distributor [Member] | Film and Electrolytic [Member]
Segment and geographic information
Net sales	18,960	24,762	41,287	51,330
Distributor [Member] | Electro-magnetic, Sensors & Actuators [Member]
Segment and geographic information
Net sales	2,559	2,707	5,123	5,192
EMS [Member]
Segment and geographic information
Net sales	51,542	50,785	105,462	92,786
EMS [Member] | Solid Capacitors
Segment and geographic information
Net sales	44,420	43,976	91,695	79,776
EMS [Member] | Film and Electrolytic [Member]
Segment and geographic information
Net sales	6,448	5,771	12,303	11,717
EMS [Member] | Electro-magnetic, Sensors & Actuators [Member]
Segment and geographic information
Net sales	674	1,038	1,464	1,293
Tantalum [Member] | Solid Capacitors
Segment and geographic information
Net sales	125,106	148,054	257,492	282,367
Ceramics [Member] | Solid Capacitors
Segment and geographic information
Net sales	$ 108,527	$ 87,419	$ 224,348	$ 166,927