Note 6 - Stock-based Compensation (Tables)

12 Months Ended

Mar. 31, 2017

Notes Tables

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

	Year Ended March 31
	2017			2016			2015
Risk-free interest rate		1.0	%		1.6	%		1.6	%
Expected volatility		27	%		26	%		24	%
Expected life (years)		4.3			4.3			4.2
Dividend yield		7.0	%		7.1	%		0	%

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		5,000	$	49.70		4.0
56.76	-	67.69		14,000		60.30		7.8
				19,000	$	57.51		6.8

Share-based Compensation, Activity [Table Text Block]

	Option Shares Reserved			Options Outstanding			Weighted Average Option Exercise Price		Warrants Outstanding			Weighted Average Warrant Exercise Price
At March 31, 2014		155,230			38,000		$	31.78		2,000		$	37.38
Granted		(4,000	)		4,000		$	67.69		-			-
Exercised		-			(6,910	)	$	43.81		-			-
Terminated		-			-		$	-		(2,000	)		37.38
At March 31, 2015		151,230			35,090		$	33.51		-		$	-
Granted		(4,000	)		4,000		$	56.76		-			-
Exercised		-			(18,090	)	$	16.19		-			-
Terminated		-			-		$	-		-			-
At March 31, 2016		147,230			21,000		$	52.85		-		$	-
Granted		(4,000	)		4,000		$	57.46		-			-
Exercised		-			(6,000	)	$	41.19		-			-
Terminated		-			-		$	-		-			-
At March 31, 2017		143,230			19,000		$	57.51		-		$	-