Note 10 - Employee Equity Incentive Plans - Fair Value and Assumptions (Details) - $ / shares	12 Months Ended
	Mar. 31, 2017		Mar. 31, 2016		Mar. 31, 2015
Employee Stock Option [Member]
Weighted average estimated fair value of grant per share (in dollars per share)	$ 4.48		$ 4.83	[1]	$ 5.54
Risk-free interest rate	1.60%		1.80%	[1]	1.80%
Expected term in years (Year)	6 years 149 days		6 years 164 days	[1]	6 years 91 days
Volatility	40.60%		44.90%	[1]	52.20%
Dividend yield	0.40%	[2]	1.20%	[1]	1.00%	[2]
Employee Stock Purchase Plan 1999 [Member]
Weighted average estimated fair value of grant per share (in dollars per share)	$ 3.28		$ 3.33	[3]	$ 2.90	[3]
Risk-free interest rate	0.40%		0.10%	[3]	0.10%	[3]
Expected term in years (Year)	273 days		182 days	[3]	182 days	[3]
Volatility	37.50%		39.80%	[3]	36.90%	[3]
Dividend yield	0.70%		1.10%	[2],[3]	1.10%	[3]

[1] No stock options were granted during the quarter ended December 31, 2015.

[2] No dividends were declared for the quarters ended September 30, 2016 and December 31, 2016.

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