Note 7 - Financial Instruments and Investments in Securities (Tables)

9 Months Ended

Dec. 31, 2018

Notes Tables

Debt Securities, Held-to-maturity [Table Text Block]

	March 31, 2018
			Gross		Gross
			Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
Short-term investments:
Commercial paper	$	10,597	$	-	$	(1	)	$	10,596
Time deposits		269,190		203		-			269,393
	$	279,787	$	203	$	(1	)	$	279,989

	December 31, 2018
			Gross		Gross
			Unrealized		Unrealized		Estimated
	Cost		Gains		Losses		Fair Value
Short-term investments:
Commercial paper	$	74,505	$	314	$	-	$	74,819
Time deposits		425,023		369		-		425,392
	$	499,528	$	683	$	-	$	500,211

Investments Classified by Contractual Maturity Date [Table Text Block]

	Held-to-Maturity
	Amortized		Estimated
	Cost		Fair Value
Due in one year or less	$	499,528	$	500,211
Due after one year through five years		-		-
Total	$	499,528	$	500,211