Segment and Geographic Information - Net Sales by Country (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales	$ 293,174	$ 294,741	$ 327,397	$ 345,242	$ 355,794	$ 350,175	$ 349,233	$ 327,616	$ 1,260,554	$ 1,382,818	$ 1,200,181
Property, plant, and equipment, net	552,636				495,280				552,636	495,280
Solid Capacitors
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									886,063	935,838	771,240
Film and Electrolytic
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									$ 175,803	$ 206,240	$ 201,977
Net sales | Sales risk
Net sales and property, plant and equipment, goodwill, intangible assets
Number of customers									1	1	1
Concentration Risk, Geographic									0	0	0
Net sales									$ 154,600	$ 184,300	$ 133,500
Net sales | Geographic risk
Net sales and property, plant and equipment, goodwill, intangible assets
Threshold for Disclosure Percentage									3.00%	3.00%	3.00%
Property, Plant and Equipment | Geographic risk
Net sales and property, plant and equipment, goodwill, intangible assets
Threshold for Disclosure Percentage									1.00%
United States
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									$ 246,821	$ 292,980	$ 233,133
Property, plant, and equipment, net	68,992				57,095				68,992	57,095
Japan
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									157,539	178,502	170,282
Property, plant, and equipment, net	89,080				89,602				89,080	89,602
THAILAND
Net sales and property, plant and equipment, goodwill, intangible assets
Property, plant, and equipment, net	82,905				82,389				82,905	82,389
China
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									181,319	173,148	163,016
Property, plant, and equipment, net	51,120				45,815				51,120	45,815
Italy
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									12,031	15,551	17,905
Property, plant, and equipment, net	25,373				35,197				25,373	35,197
Hungary
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									12,050	12,245	13,254
Mexico
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									49,346	44,267	23,915
Property, plant, and equipment, net	176,417				121,147				176,417	121,147
Other
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									1,865	1,281	2,278
Property, plant, and equipment, net	6,946				8,977				6,946	8,977
Portugal
Net sales and property, plant and equipment, goodwill, intangible assets
Property, plant, and equipment, net	33,092				31,872				33,092	31,872
Macedonia
Net sales and property, plant and equipment, goodwill, intangible assets
Property, plant, and equipment, net	12,135				12,906				12,135	12,906
BULGARIA
Net sales and property, plant and equipment, goodwill, intangible assets
Property, plant, and equipment, net	6,014				5,480				6,014	5,480
Sweden
Net sales and property, plant and equipment, goodwill, intangible assets
Property, plant, and equipment, net	562				4,800				562	4,800
Total Non-United States
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									1,013,733	1,089,838	967,048
Property, plant, and equipment, net	$ 483,644				$ 438,185				483,644	438,185
Hong Kong
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									195,898	188,102	169,073
Germany
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									99,166	124,805	105,548
Europe
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									84,504	76,149	64,248
Taiwan
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									58,364	88,853	78,728
Asia [Member]
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									46,455	47,233	36,647
United Kingdom
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									29,070	42,472	37,038
Netherlands
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									39,329	44,065	39,684
Malaysia
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									23,750	33,748	28,165
Singapore
Net sales and property, plant and equipment, goodwill, intangible assets
Net sales									$ 23,047	$ 19,417	$ 17,267
Minimum | Net sales | Sales risk
Net sales and property, plant and equipment, goodwill, intangible assets
Concentration risk, percentage									10.00%	10.00%	10.00%