Note 10 - Stockholders' Equity (Deficit) - Options Outstanding and Exercisable, by Exercise Range (Details) shares in Thousands	9 Months Ended
	Dec. 31, 2018 $ / shares shares
Lower range of exercise price (in dollars per share)	$ 0.78
Upper range of exercise price (in dollars per share)	$ 7.20
Options outstanding, number of shares (in shares) | shares	4,101
Options outstanding, weighted-average remaining contractual life (Year)	7 years 36 days
Options vested, number of shares (in shares) | shares	2,881
Options vested, weighted-average exercise price per share (in dollars per share)	$ 2.87
Range 1 [Member]
Lower range of exercise price (in dollars per share)	0.78
Upper range of exercise price (in dollars per share)	$ 1.53
Options outstanding, number of shares (in shares) | shares	324
Options outstanding, weighted-average remaining contractual life (Year)	8 years 135 days
Options vested, number of shares (in shares) | shares	114
Options vested, weighted-average exercise price per share (in dollars per share)	$ 1.28
Range 2 [Member]
Lower range of exercise price (in dollars per share)	1.64
Upper range of exercise price (in dollars per share)	$ 1.64
Options outstanding, number of shares (in shares) | shares	1,892
Options outstanding, weighted-average remaining contractual life (Year)	7 years 32 days
Options vested, number of shares (in shares) | shares	1,330
Options vested, weighted-average exercise price per share (in dollars per share)	$ 1.64
Range 3 [Member]
Lower range of exercise price (in dollars per share)	1.75
Upper range of exercise price (in dollars per share)	$ 1.81
Options outstanding, number of shares (in shares) | shares	484
Options outstanding, weighted-average remaining contractual life (Year)	8 years 58 days
Options vested, number of shares (in shares) | shares	252
Options vested, weighted-average exercise price per share (in dollars per share)	$ 1.79
Range 4 [Member]
Lower range of exercise price (in dollars per share)	2
Upper range of exercise price (in dollars per share)	$ 3.99
Options outstanding, number of shares (in shares) | shares	374
Options outstanding, weighted-average remaining contractual life (Year)	7 years 14 days
Options vested, number of shares (in shares) | shares	275
Options vested, weighted-average exercise price per share (in dollars per share)	$ 3.27
Range 5 [Member]
Lower range of exercise price (in dollars per share)	3.44
Upper range of exercise price (in dollars per share)	$ 4.32
Options outstanding, number of shares (in shares) | shares	627
Options outstanding, weighted-average remaining contractual life (Year)	6 years 211 days
Options vested, number of shares (in shares) | shares	535
Options vested, weighted-average exercise price per share (in dollars per share)	$ 4.32
Range 6 [Member]
Lower range of exercise price (in dollars per share)	4.32
Upper range of exercise price (in dollars per share)	$ 5.99
Options outstanding, number of shares (in shares) | shares	123
Options outstanding, weighted-average remaining contractual life (Year)	4 years 215 days
Options vested, number of shares (in shares) | shares	124
Options vested, weighted-average exercise price per share (in dollars per share)	$ 5.68
Range 7 [Member]
Lower range of exercise price (in dollars per share)	5.18
Upper range of exercise price (in dollars per share)	$ 6.14
Options outstanding, number of shares (in shares) | shares	213
Options outstanding, weighted-average remaining contractual life (Year)	6 years 164 days
Options vested, number of shares (in shares) | shares	187
Options vested, weighted-average exercise price per share (in dollars per share)	$ 6.14
Range 8 [Member]
Lower range of exercise price (in dollars per share)	6.61
Upper range of exercise price (in dollars per share)	$ 6.30
Options outstanding, number of shares (in shares) | shares	23
Options outstanding, weighted-average remaining contractual life (Year)	4 years 317 days
Options vested, number of shares (in shares) | shares	23
Options vested, weighted-average exercise price per share (in dollars per share)	$ 6.30
Range 9 [Member]
Lower range of exercise price (in dollars per share)	6.83
Upper range of exercise price (in dollars per share)	$ 6.61
Options outstanding, number of shares (in shares) | shares	36
Options outstanding, weighted-average remaining contractual life (Year)	2 years 204 days
Options vested, number of shares (in shares) | shares	36
Options vested, weighted-average exercise price per share (in dollars per share)	$ 6.61
Range 10 [Member]
Lower range of exercise price (in dollars per share)	7.20
Upper range of exercise price (in dollars per share)	$ 7.20
Options outstanding, number of shares (in shares) | shares	5
Options outstanding, weighted-average remaining contractual life (Year)	58 days
Options vested, number of shares (in shares) | shares	5
Options vested, weighted-average exercise price per share (in dollars per share)	$ 7.20