Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance at Mar. 31, 2018	$ 44,586	$ 111	$ 278,595	$ (234,120)
Beginning balance, Shares at Mar. 31, 2018		111,033,000
Stock option exercises	$ 50	$ 1	49	0
Stock option exercises, Shares	622,192	622,000
Issuance of common stock under employee and director stock option, RSU and purchase plans	$ (139)	$ 1	(140)	0
Issuance of common stock under employee and director stock option, RSU and purchase plans, Shares		728,000
Stock-based compensation expense	5,193	$ 0	5,193	0
Issuance of common stock from public offering, net	13,243	$ 11	13,232	0
Issuance of common stock from public offering, Shares		11,632,000
Net loss	(26,635)	$ 0	0	(26,635)
Ending balance at Mar. 31, 2019	$ 36,298	$ 124	296,929	(260,755)
Ending balance, Shares at Mar. 31, 2019		124,015,000
Stock option exercises, Shares	0
Issuance of common stock under employee and director stock option, RSU and purchase plans	$ (61)	$ 1	(62)	0
Issuance of common stock under employee and director stock option, RSU and purchase plans, Shares		456,000
Stock-based compensation expense	4,108	$ 0	4,108	0
Issuance of common stock from public offering, net	4,996	$ 6	4,990	0
Issuance of common stock from public offering, Shares		6,087,000
Net loss	(18,710)	$ 0	0	(18,710)
Ending balance at Mar. 31, 2020	$ 26,631	$ 131	$ 305,965	$ (279,465)
Ending balance, Shares at Mar. 31, 2020		130,558,000