Note 10 - Segment and Geographic Information - Reportable Segment Revenue, Profit and Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2019
Net Sales	$ 344,441	$ 442,395	$ 1,123,496	$ 1,352,839
Operating profit (loss)	35,869	89,556	132,028	243,211
Assets	2,835,720		2,835,720		$ 2,813,278
Goodwill	324,395		324,395		316,675
Operating Segments [Member] | Electronic Components [Member]
Net Sales	230,544	326,072	764,666	977,513
Operating profit (loss)	58,093	115,787	197,924	306,332
Assets	794,697		794,697		659,933
Operating Segments [Member] | Electronic Components [Member] | Ceramic Components [Member]
Net Sales	72,522	120,561	267,042	302,075
Operating Segments [Member] | Electronic Components [Member] | Tantalum Components [Member]
Net Sales	55,376	95,167	177,550	301,901
Operating Segments [Member] | Electronic Components [Member] | Advanced Components [Member]
Net Sales	102,646	110,344	320,074	373,537
Operating Segments [Member] | Interconnect, Sensing and Control Devices [Member]
Net Sales	113,897	116,323	358,830	375,326
Operating profit (loss)	(2,906)	1,883	(6,342)	1,416
Assets	286,011		286,011		265,682
Segment Reconciling Items [Member]
Cash, A/R, and investments in securities	955,866		955,866		1,070,701
Segment Reconciling Items [Member] | Electronic Components [Member]
Goodwill	279,561		279,561		271,374
Segment Reconciling Items [Member] | Interconnect, Sensing and Control Devices [Member]
Goodwill	44,834		44,834		45,301
Corporate, Non-Segment [Member]
Operating profit (loss)	(19,318)	$ (28,114)	(59,554)	$ (64,537)
Assets	$ 474,751		$ 474,751		$ 500,287