Note 11 - Segment and Geographic Information - Reportable Segment Revenue, Profit and Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Net sales	$ 442,395	$ 431,795	$ 1,352,839	$ 1,115,842
Operating profit (loss)	89,556	45,331	243,211	132,548
Total Assets	2,769,530		2,769,530		$ 2,672,766
Goodwill	317,676		317,676		316,298
Operating Segments [Member] | Electronic Components [Member]
Net sales	326,072	306,567	977,513	928,353
Operating profit (loss)	115,787	54,880	306,332	165,675
Total Assets	723,804		723,804		632,014
Operating Segments [Member] | Electronic Components [Member] | Ceramic Components [Member]
Net sales	120,561	60,136	302,075	168,512
Operating Segments [Member] | Electronic Components [Member] | Tantalum Components [Member]
Net sales	95,167	90,517	301,901	273,457
Operating Segments [Member] | Electronic Components [Member] | Advanced Components [Member]
Net sales	110,344	155,914	373,537	486,384
Operating Segments [Member] | Interconnect, Sensing and Control Devices [Member]
Net sales	116,323	125,228	375,326	187,489
Operating profit (loss)	1,883	6,637	1,416	13,281
Total Assets	250,798		250,798		241,959
Segment Reconciling Items [Member]
Cash, A/R, and investments in securities	1,103,886		1,103,886		1,111,716
Segment Reconciling Items [Member] | Electronic Components [Member]
Goodwill	281,806		281,806		278,247
Segment Reconciling Items [Member] | Interconnect, Sensing and Control Devices [Member]
Goodwill	35,870		35,870		38,051
Corporate, Non-Segment [Member]
Operating profit (loss)	(28,114)	$ (16,186)	(64,537)	$ (46,408)
Total Assets	$ 373,366		$ 373,366		$ 370,779