Condensed Consolidating Financial Statements Balance Sheet (Details) - USD ($) $ in Thousands	9 Months Ended
	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Current assets:
Cash and cash equivalents	$ 87,356	$ 65,004	$ 43,158	$ 56,362
Accounts receivable, net	82,519	93,168
Intercompany receivable	0	0
Inventories, net	154,519	168,879
Prepaid expenses and other	24,035	25,496
Total current assets	348,429	352,547
Assets, Noncurrent [Abstract]
Property and equipment, net	211,927	241,839
Goodwill	40,294	40,294
Intangible assets, net	30,204	33,301
Investment in NEC TOKIN	21,202	20,334
Investments in subsidiaries	0	0
Deferred income taxes	7,768	8,397
Other assets	2,712	3,068
Long-term intercompany receivable	0	0
Total assets	662,536	699,780
Current liabilities:
Current portion of long-term debt	0	2,000
Accounts payable	62,347	70,981
Intercompany payable	0	0
Accrued expenses	46,418	50,320
Income taxes payable	1,068	453
Total current liabilities	109,833	123,754
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	386,226	385,833
Other non-current obligations	72,704	74,892
Deferred income taxes	3,326	2,820
Long-term intercompany payable	0	0
Stockholders’ equity	90,447	112,481
Total liabilities and stockholders’ equity	662,536	699,780
Reclassifications and Eliminations
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Intercompany receivable	(377,917)	(332,957)
Inventories, net	0	0
Prepaid expenses and other	(2,964)	(2,964)
Total current assets	(380,881)	(335,921)
Assets, Noncurrent [Abstract]
Property and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Investment in NEC TOKIN	0	0
Investments in subsidiaries	(915,622)	(905,190)
Deferred income taxes	0	0
Other assets	0	0
Long-term intercompany receivable	(101,941)	(110,016)
Total assets	(1,398,444)	(1,351,127)
Current liabilities:
Current portion of long-term debt		0
Accounts payable	0	0
Intercompany payable	(377,917)	(332,957)
Accrued expenses	0	0
Income taxes payable	(2,964)	(2,964)
Total current liabilities	(380,881)	(335,921)
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	0	0
Other non-current obligations	0	0
Deferred income taxes	0	0
Long-term intercompany payable	(101,941)	(110,016)
Stockholders’ equity	(915,622)	(905,190)
Total liabilities and stockholders’ equity	(1,398,444)	(1,351,127)
Parent
Current assets:
Cash and cash equivalents	729	640	640	640
Accounts receivable, net	0	0
Intercompany receivable	32,874	30,210
Inventories, net	0	0
Prepaid expenses and other	3,325	3,325
Total current assets	36,928	34,175
Assets, Noncurrent [Abstract]
Property and equipment, net	498	255
Goodwill	0	0
Intangible assets, net	0	0
Investment in NEC TOKIN	0	0
Investments in subsidiaries	394,561	382,108
Deferred income taxes	0	0
Other assets	27	0
Long-term intercompany receivable	62,496	67,500
Total assets	494,510	484,038
Current liabilities:
Current portion of long-term debt		2,000
Accounts payable	40	20
Intercompany payable	42,935	280
Accrued expenses	8,743	17,305
Income taxes payable	0	0
Total current liabilities	51,718	19,605
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	352,345	351,952
Other non-current obligations	0	0
Deferred income taxes	0	0
Long-term intercompany payable	0	0
Stockholders’ equity	90,447	112,481
Total liabilities and stockholders’ equity	494,510	484,038
Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	46,038	36,209	18,643	33,094
Accounts receivable, net	26,500	41,025
Intercompany receivable	195,280	132,523
Inventories, net	102,559	113,289
Prepaid expenses and other	11,976	12,161
Total current assets	382,353	335,207
Assets, Noncurrent [Abstract]
Property and equipment, net	81,692	93,936
Goodwill	40,294	40,294
Intangible assets, net	25,020	27,252
Investment in NEC TOKIN	21,202	20,334
Investments in subsidiaries	427,702	429,723
Deferred income taxes	1,045	800
Other assets	1,779	2,452
Long-term intercompany receivable	38,356	41,428
Total assets	1,019,443	991,426
Current liabilities:
Current portion of long-term debt		0
Accounts payable	30,601	34,618
Intercompany payable	270,738	275,498
Accrued expenses	19,334	11,807
Income taxes payable	3,007	2,983
Total current liabilities	323,680	324,906
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	19,881	19,881
Other non-current obligations	27,399	25,797
Deferred income taxes	2,556	2,242
Long-term intercompany payable	62,496	67,500
Stockholders’ equity	583,431	551,100
Total liabilities and stockholders’ equity	$ 1,019,443	991,426
Guarantor Subsidiaries | Reportable legal entities
Condensed Consolidating Balance Sheet
Percentage of ownership interest	100.00%
Non-Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	$ 40,589	28,155	$ 23,875	$ 22,628
Accounts receivable, net	56,019	52,143
Intercompany receivable	149,763	170,224
Inventories, net	51,960	55,590
Prepaid expenses and other	11,698	12,974
Total current assets	310,029	319,086
Assets, Noncurrent [Abstract]
Property and equipment, net	129,737	147,648
Goodwill	0	0
Intangible assets, net	5,184	6,049
Investment in NEC TOKIN	0	0
Investments in subsidiaries	93,359	93,359
Deferred income taxes	6,723	7,597
Other assets	906	616
Long-term intercompany receivable	1,089	1,088
Total assets	547,027	575,443
Current liabilities:
Current portion of long-term debt		0
Accounts payable	31,706	36,343
Intercompany payable	64,244	57,179
Accrued expenses	18,341	21,208
Income taxes payable	1,025	434
Total current liabilities	115,316	115,164
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	14,000	14,000
Other non-current obligations	45,305	49,095
Deferred income taxes	770	578
Long-term intercompany payable	39,445	42,516
Stockholders’ equity	332,191	354,090
Total liabilities and stockholders’ equity	$ 547,027	$ 575,443
10.5% Senior Notes, net [Member]
Condensed Consolidating Balance Sheet
Interest rate of senior notes (as a percent)	10.50%
10.5% Senior Notes, net [Member] | Non-Guarantor Subsidiaries
Condensed Consolidating Balance Sheet
Percentage of capital stock	51.00%