CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $)	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Beginning Balance, Value at Apr. 30, 2010	$ 53,000	$ 275,208,000	$ (261,854,000)	$ 13,407,000
Beginning Balance, Shares at Apr. 30, 2010	53,094,896
Common stock issued for cash, net of issuance costs, Shares	16,364,429
Common stock issued for cash, net of issuance costs, Value	17,000	33,070,000		33,087,000
Common stock issued upon exercise of options, Shares	20,750
Common stock issued upon exercise of options, Value		44,000		44,000
Common stock issued upon exercise of warrants, Shares	74,802
Common stock issued upon exercise of warrants, Value
Common stock issued for services, Shares	28,921
Common stock issued for services, Value		60,000		60,000
Common stock issued under restricted stock awards, Shares	148,500
Common stock issued under restricted stock awards, Value
Common stock issued under Employee Stock Purchase Plan, Shares	104,844
Common stock issued under Employee Stock Purchase Plan, Value		134,000		134,000
Share-based compensation		2,837,000		2,837,000
Net loss			(34,151,000)	(34,151,000)
Ending Balance, Value at Apr. 30, 2011	70,000	311,353,000	(296,005,000)	15,418,000
Ending Balance, Shares at Apr. 30, 2011	69,837,142
Common stock issued for cash, net of issuance costs, Shares	31,126,182
Common stock issued for cash, net of issuance costs, Value	31,000	33,148,000		33,179,000
Common stock issued under Employee Stock Purchase Plan, Shares	458,041
Common stock issued under Employee Stock Purchase Plan, Value		236,000		236,000
Share-based compensation		2,769,000		2,769,000
Net loss			(42,119,000)	(42,119,000)
Ending Balance, Value at Apr. 30, 2012	101,000	347,506,000	(338,124,000)	9,483,000
Ending Balance, Shares at Apr. 30, 2012	101,421,365
Common stock issued for cash, net of issuance costs, Shares	41,184,043
Common stock issued for cash, net of issuance costs, Value	41,000	39,481,000		39,522,000
Common stock issued upon exercise of options, Shares	118,555			(118,555)
Common stock issued upon exercise of options, Value		96,000		96,000
Common stock issued upon exercise of warrants, Shares	46,427
Common stock issued upon exercise of warrants, Value
Common stock issued under Employee Stock Purchase Plan, Shares	998,556
Common stock issued under Employee Stock Purchase Plan, Value	1,000	533,000		534,000
Fair market value of warrants issued with notes payable		470,000		470,000
Share-based compensation		3,435,000		3,435,000
Net loss			(29,780,000)	(29,780,000)
Ending Balance, Value at Apr. 30, 2013	$ 143,000	$ 391,521,000	$ (367,904,000)	$ 23,760,000
Ending Balance, Shares at Apr. 30, 2013	143,768,946