Note 6 - Stock-based Compensation (Tables)

12 Months Ended

Mar. 31, 2018

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended March 31
	2018			2017			2016
Risk-free interest rate		1.8	%		1.0	%		1.6	%
Expected volatility		28	%		27	%		26	%
Expected life (years)		4.4			4.3			4.3
Dividend yield		5.3	%		7.0	%		7.1	%

Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]

Ranges of Exercise Prices			Number Outstanding		Weighted Average Exercise Price		Weighted Remaining Contractual Life (years)
$42.45	-	54.11		4,000	$	49.37		3.4
56.76	-	76.13		18,000		63.81		7.4
				22,000	$	61.19		6.6

Share-based Compensation, Activity [Table Text Block]

	Option Shares Reserved			Options Outstanding			Weighted Average Option Exercise Price
At March 31, 2015		151,230			35,090		$	33.51
Granted		(4,000	)		4,000		$	56.76
Exercised		-			(18,090	)	$	16.19
At March 31, 2016		147,230			21,000		$	52.85
Granted		(4,000	)		4,000		$	57.46
Exercised		-			(6,000	)	$	41.19
At March 31, 2017		143,230			19,000		$	57.51
Granted		(4,000	)		4,000		$	76.13
Exercised		-			(1,000	)	$	51.04
At March 31, 2018		139,230			22,000		$	61.19