Note 10 - Employee Equity Incentive Plans - Fair Value and Assumptions (Details) - $ / shares		3 Months Ended		6 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Stock Option [Member]
Weighted average estimated fair value of grant per share (in dollars per share)		$ 4.31	$ 5.54	$ 4.83	$ 5.54
Risk-free interest rate		1.70%	1.80%	1.80%	1.80%
Expected term in years		6 years 127 days	6 years 91 days	6 years 164 days	6 years 91 days
Volatility		42.80%	52.20%	44.90%	52.20%
Dividend yield		1.30%	1.00%	1.20%	1.00%
Employee Stock Purchase Plan 1999 [Member]
Weighted average estimated fair value of grant per share (in dollars per share)	[1]			$ 3.15	$ 2.90
Risk-free interest rate	[1]			0.10%	0.10%
Expected term in years	[1]			1 year	182 days
Volatility	[1]			33.70%	34.50%
Dividend yield	[1]			1.10%	1.10%

[1] Under the stock purchase plan, rights to purchase shares are only granted during the first and third quarters of each fiscal year.