Condensed Consolidating Financial Statements Balance Sheet (Details) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Current assets:
Cash and cash equivalents	$ 74,753	$ 65,004	$ 37,315	$ 56,362	$ 56,362
Accounts receivable, net	88,089	93,168
Intercompany receivable	0	0
Inventories, net	164,977	168,879
Prepaid expenses and other	30,990	25,496
Total current assets	358,809	352,547
Assets, Noncurrent [Abstract]
Property and equipment, net	221,490	241,839
Goodwill	40,294	40,294
Intangible assets, net	30,993	33,301
Investment in NEC TOKIN	15,174	20,334
Investments in subsidiaries	0	0
Deferred income taxes	7,749	8,397
Other assets	2,466	3,068
Long-term intercompany receivable	0	0
Total assets	676,975	699,780
Current liabilities:
Current portion of long-term debt	0	2,000
Accounts payable	64,055	70,981
Intercompany payable	0	0
Accrued expenses	58,015	50,320
Income taxes payable	293	453
Total current liabilities	122,363	123,754
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	386,098	385,833
Other non-current obligations	82,640	74,892
Deferred income taxes	2,994	2,820
Long-term intercompany payable	0	0
Stockholders’ equity	82,880	112,481
Total liabilities and stockholders’ equity	676,975	699,780
Reclassifications and Eliminations
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Intercompany receivable	(350,243)	(332,957)
Inventories, net	0	0
Prepaid expenses and other	(2,964)	(2,964)
Total current assets	(353,207)	(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	(894,233)	(905,190)
Deferred income taxes	0	0
Other assets	0	0
Long-term intercompany receivable	(107,873)	(110,016)
Total assets	(1,355,313)	(1,351,127)
Current liabilities:
Current portion of long-term debt		0
Accounts payable	0	0
Intercompany payable	(350,243)	(332,957)
Accrued expenses	0	0
Income taxes payable	(2,964)	(2,964)
Total current liabilities	(353,207)	(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	(107,873)	(110,016)
Stockholders’ equity	(894,233)	(905,190)
Total liabilities and stockholders’ equity	(1,355,313)	(1,351,127)
Parent
Current assets:
Cash and cash equivalents	623	640	640	640
Accounts receivable, net	0	0
Intercompany receivable	31,782	30,210
Inventories, net	0	0
Prepaid expenses and other	3,325	3,325
Total current assets	35,730	34,175
Assets, Noncurrent [Abstract]
Property and equipment, net	514	255
Goodwill	0	0
Intangible assets, net	0	0
Investment in NEC TOKIN	0	0
Investments in subsidiaries	373,172	382,108
Deferred income taxes	0	0
Other assets	27	0
Long-term intercompany receivable	66,172	67,500
Total assets	475,615	484,038
Current liabilities:
Current portion of long-term debt		2,000
Accounts payable	29	20
Intercompany payable	23,243	280
Accrued expenses	17,246	17,305
Income taxes payable	0	0
Total current liabilities	40,518	19,605
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	352,217	351,952
Other non-current obligations	0	0
Deferred income taxes	0	0
Long-term intercompany payable	0	0
Stockholders’ equity	82,880	112,481
Total liabilities and stockholders’ equity	475,615	484,038
Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	48,399	36,209	22,035	33,094
Accounts receivable, net	32,116	41,025
Intercompany receivable	164,695	132,523
Inventories, net	107,191	113,289
Prepaid expenses and other	18,219	12,161
Total current assets	370,620	335,207
Assets, Noncurrent [Abstract]
Property and equipment, net	82,229	93,936
Goodwill	40,294	40,294
Intangible assets, net	25,357	27,252
Investment in NEC TOKIN	15,174	20,334
Investments in subsidiaries	427,702	429,723
Deferred income taxes	755	800
Other assets	1,643	2,452
Long-term intercompany receivable	40,612	41,428
Total assets	1,004,386	991,426
Current liabilities:
Current portion of long-term debt		0
Accounts payable	33,084	34,618
Intercompany payable	272,187	275,498
Accrued expenses	19,107	11,807
Income taxes payable	2,996	2,983
Total current liabilities	327,374	324,906
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	19,881	19,881
Other non-current obligations	35,112	25,797
Deferred income taxes	2,242	2,242
Long-term intercompany payable	66,172	67,500
Stockholders’ equity	553,605	551,100
Total liabilities and stockholders’ equity	$ 1,004,386	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	$ 25,731	28,155	$ 14,640	$ 22,628
Accounts receivable, net	55,973	52,143
Intercompany receivable	153,766	170,224
Inventories, net	57,786	55,590
Prepaid expenses and other	12,410	12,974
Total current assets	305,666	319,086
Assets, Noncurrent [Abstract]
Property and equipment, net	138,747	147,648
Goodwill	0	0
Intangible assets, net	5,636	6,049
Investment in NEC TOKIN	0	0
Investments in subsidiaries	93,359	93,359
Deferred income taxes	6,994	7,597
Other assets	796	616
Long-term intercompany receivable	1,089	1,088
Total assets	552,287	575,443
Current liabilities:
Current portion of long-term debt		0
Accounts payable	30,942	36,343
Intercompany payable	54,813	57,179
Accrued expenses	21,662	21,208
Income taxes payable	261	434
Total current liabilities	107,678	115,164
Liabilities, Noncurrent [Abstract]
Long-term debt, less current portion	14,000	14,000
Other non-current obligations	47,528	49,095
Deferred income taxes	752	578
Long-term intercompany payable	41,701	42,516
Stockholders’ equity	340,628	354,090
Total liabilities and stockholders’ equity	$ 552,287	$ 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%