Segment and Geographic Information Segment and Geographic Information - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Segment and geographic information
Assets	$ 1,393,097				$ 1,318,095				$ 1,393,097	$ 1,318,095
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									(800)	1,000	$ 1,200
Asset Impairment Charges									18,900	700	200
Restructuring charges									8,882	8,779	14,843
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down									19,710	1,660	(992)
Operating income (loss)	11,728	$ 28,648	$ 49,090	$ 58,400	54,057	$ 61,616	$ 50,000	$ 35,176	147,866	200,849	112,852
Depreciation and amortization									62,819	52,628	50,661
Additions to Other Assets, Amount									146,331	146,056	65,004
Solid Capacitors
Segment and geographic information
Assets	888,046				794,402				888,046	794,402
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property											(600)
Restructuring charges									517	4,922	983
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down									1,538	235	689
Operating income (loss)									345,245	348,150	234,473
Depreciation and amortization									33,462	28,795	27,329
Additions to Other Assets, Amount									102,600	80,700	31,249
Film and Electrolytic
Segment and geographic information
Assets	207,601				219,711				207,601	219,711
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property											(3,600)
Restructuring charges									3,458	2,717	5,788
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down									7,780	(93)	(3,356)
Operating income (loss)									(14,209)	8,183	3,622
Depreciation and amortization									10,142	9,763	10,918
Additions to Other Assets, Amount									9,900	16,000	12,651
Electro-magnetic, Sensors & Actuators [Member]
Segment and geographic information
Assets	220,107				234,419				220,107	234,419
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property											(1,300)
Restructuring charges									3,516	452	3,343
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down									0	0	1,272
Operating income (loss)									13,101	22,546	15,694
Depreciation and amortization									7,379	5,226	4,407
Additions to Other Assets, Amount									10,600	13,400	8,481
Corporate
Segment and geographic information
Assets	$ 77,343				$ 69,563				77,343	69,563
Asset Impairment Charges									8,900
Restructuring charges									1,391	688	4,729
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down									10,392	1,518	403
Operating income (loss)									(196,271)	(178,030)	(140,937)
Depreciation and amortization									11,836	8,844	8,007
Additions to Other Assets, Amount									$ 23,231	$ 35,956	$ 12,623