Segment and Geographic Information Segment and Geographic Information - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Segment and geographic information
Assets	$ 734,528				$ 699,780				$ 734,528	$ 699,780
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									(392)	(375)	$ 221
Asset Impairment Charges									10,279	0	0
Restructuring charges									5,404	4,178	13,017
Net sales	197,519	$ 188,029	$ 187,308	$ 184,935	183,926	$ 177,184	$ 186,123	$ 187,590	757,791	734,823	823,192
Operating income (loss)	8,742	$ 13,850	$ 3,050	$ 8,898	8,603	$ 8,493	$ 13,987	$ 1,243	34,540	32,326	22,378
Depreciation and amortization									37,338	39,016	40,768
Additions to Other Assets, Amount									25,617	20,469	22,232
Solid Capacitors [Member]
Segment and geographic information
Assets	439,281				424,659				439,281	424,659
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									(227)	(536)	(606)
Asset Impairment Charges										0	0
Restructuring charges									1,333	1,916	3,297
Net sales									575,110	556,303	621,275
Operating income (loss)									146,694	129,909	135,946
Depreciation and amortization									20,824	21,318	21,202
Additions to Other Assets, Amount									12,300	10,098	12,552
Film and Electrolytic
Segment and geographic information
Assets	204,407				234,822				204,407	234,822
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									(136)	270	1,008
Asset Impairment Charges									8,200	0	0
Restructuring charges									3,738	1,714	8,221
Net sales									182,681	178,520	201,917
Operating income (loss)									(8,278)	(71)	(16,685)
Depreciation and amortization									10,953	11,984	13,886
Additions to Other Assets, Amount									7,955	5,902	7,752
Corporate
Segment and geographic information
Assets	$ 90,840				$ 40,299				90,840	40,299
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									(29)	(109)	(181)
Restructuring charges									333	548	1,499
Operating income (loss)									(103,876)	(97,512)	(96,883)
Depreciation and amortization									5,561	5,714	5,680
Additions to Other Assets, Amount									$ 5,362	$ 4,469	$ 1,928