Equity Method Investments - Reconciliation (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 12,016	$ 63,416
Nippon Yttrium Co., Ltd (NYC)
Schedule of Equity Method Investments [Line Items]
Equity method investments	8,148	0
NT Sales Co., Ltd (NTS)
Schedule of Equity Method Investments [Line Items]
Equity method investments	998	0
Investment in Novasentis
Schedule of Equity Method Investments [Line Items]
Equity method investments	2,870	0
Investment in TOKIN
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 0	$ 63,416