Note 9 - Employee Equity Incentive Plans - Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	6 Months Ended
		Sep. 30, 2017	Sep. 30, 2017	Mar. 31, 2017
Options outstanding, beginning of period (in shares)			5,097,545
Weighted average exercise price per share, beginning balance (in dollars per share)			$ 10.71
Options oustanding, Options granted (in shares)		0	549,000
Weighted average exercise price per share, Options granted (in dollars per share)			$ 16.05
Options oustanding, Options exercised (in shares)			(1,059,795)
Weighted average exercise price per share, Options exercised (in dollars per share)			$ 9.72
Options exercised, Intrinsic Value	[1]		$ 8,074
Options oustanding, Options cancelled (in shares)			(89,750)
Weighted average exercise price per share, Options cancelled (in dollars per share)			$ 11.42
Options oustanding, Options expired (in shares)			(20,250)
Weighted average exercise price per share, Options expired (in dollars per share)			$ 9.46
Options oustanding, ending balance (in shares)		4,476,750	4,476,750
Weighted average exercise price per share, ending balance (in dollars per share)		$ 11.59	$ 11.59
Options exercisable (in shares)		2,717,250	2,717,250	3,300,295
Weighted average exercise price per share, exercisable (in dollars per share)		$ 10.80	$ 10.80	$ 10.34

[1] Represents the difference between the exercise price and the value of our common stock at the time of exercise.