Note 10 - Employee Equity Incentive Plans - Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Shares available for grant, beginning balance (in shares)		637,500	1,747,000	1,930,250
Options outstanding, beginning balance (in shares)	[1]	5,234,397	4,942,511	5,201,635
Weighted average exercise price per share, beginning balance (in dollars per share)		$ 10.40	$ 10.37	$ 10.22
Options outstanding, intrinsic value	[2]	$ 19,570	$ 6,456	$ 10,831	$ 8,658
New shares authorized (3) (in shares)	[3]	2,000,000
Shares available for grant, options granted (in shares)		(746,000)	(1,124,000)	(249,000)
Options granted (in shares)	[1]	746,000	1,124,000	249,000
Weighted average exercise price per share, options granted (in dollars per share)		$ 11.06	$ 11.72	$ 11.83
Options exercised (in shares)	[1]	(859,852)	(382,826)	(339,374)
Options exercised, intrinsic value	[2]	$ 3,112	$ 1,551	$ 1,310
Weighted average exercise price per share, options exercised (in dollars per share)		$ 9.10	$ 9.02	$ 8.62
Shares available for grant, options cancelled (in shares)		7,500	14,500	39,750
Options cancelled (in shares)	[1]	(7,500)	(14,500)	(94,250)
Weighted average exercise price per share, options cancelled (in dollars per share)		$ 13.37	$ 11.31	$ 11.46
Shares available for grant, options expired (in shares)		22,500		26,000
Options expired (in shares)	[1]	(27,500)	(434,788)	(74,500)
Weighted average exercise price per share, options expired (in dollars per share)		$ 11.81	$ 14.68	$ 11.17
Shares available for grant, ending balance (in shares)		1,921,500	637,500	1,747,000
Options outstanding, ending balance (in shares)	[1]	5,085,545	5,234,397	4,942,511
Weighted average exercise price per share, ending balance (in dollars per share)		$ 10.70	$ 10.40	$ 10.37

[1] The number of stock options exercised includes shares that were withheld on behalf of employees to satisfy the statutory tax withholding requirements.

[2] Except for options exercised, these amounts represent the difference between the exercise price and $14.55 per share, the closing price of our stock on March 31, 2017 as reported on the NASDAQ Global Select Market, for all in-the-money, outstanding and exercisable options.

[3] On August 26, 2016, our stockholders approved the 2016 Plan, under which 2,000,000 shares of our common stock are reserved for the grant of stock options and other equity incentives.