Note 11 - Employee Equity Incentive Plans - Fair Value and Assumptions (Details) - $ / shares		3 Months Ended			6 Months Ended
		Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Stock Option [Member]
Weighted average estimated fair value of grant per share (in dollars per share)		$ 4.99		$ 4.31	$ 4.40	$ 4.83
Risk-free interest rate		1.30%		1.70%	1.30%	1.80%
Expected term in years		6 years 149 days		6 years 127 days	6 years 149 days	6 years 164 days
Volatility		42.00%		42.80%	41.40%	44.90%
Dividend yield			[1]	1.30%	0.80%	1.20%
Employee Stock Purchase Plan 1999 [Member]
Weighted average estimated fair value of grant per share (in dollars per share)	[2]				$ 3.94	$ 3.15
Risk-free interest rate	[2]				0.30%	0.10%
Expected term in years	[2]				1 year	1 year
Volatility	[2]				42.90%	33.70%
Dividend yield	[2]				1.40%	1.10%

[1] No dividends were declared for the quarter ended September 30, 2016.

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