CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Beginning balance, shares at Apr. 30, 2013	0	143,768,946
Beginning balance, value at Apr. 30, 2013	$ 0	$ 143,000	$ 391,521,000	$ (367,904,000)	$ 23,760,000
Series E preferred stock issued for cash, net of issuance costs, shares	775,000
Series E preferred stock issued for cash, net of issuance costs, value	$ 1,000		17,916,000		17,917,000
Series E preferred stock dividends			(232,000)		(232,000)
Common stock issued for cash, net of issuance costs, shares		33,527,369
Common stock issued for cash, net of issuance costs, value		$ 34,000	53,886,000		53,920,000
Common stock issued under Employee Stock Purchase Plan, shares		498,050
Common stock issued under Employee Stock Purchase Plan, value		$ 1,000	544,000		545,000
Common stock issued upon exercise of options, shares		976,799
Common stock issued upon exercise of options, value		$ 1,000	943,000		944,000
Common stock issued under restricted stock awards, shares		100,000
Share-based compensation			6,207,000		6,207,000
Net loss				(35,362,000)	(35,362,000)
Ending balance, shares at Apr. 30, 2014	775,000	178,871,164
Ending balance, value at Apr. 30, 2014	$ 1,000	$ 179,000	470,785,000	(403,266,000)	67,699,000
Series E preferred stock issued for cash, net of issuance costs, shares	799,764
Series E preferred stock issued for cash, net of issuance costs, value	$ 1,000		18,202,000		18,203,000
Series E preferred stock dividends			(3,352,000)		(3,352,000)
Common stock issued for cash, net of issuance costs, shares		13,665,117
Common stock issued for cash, net of issuance costs, value		$ 14,000	19,221,000		19,235,000
Common stock issued under Employee Stock Purchase Plan, shares		497,453
Common stock issued under Employee Stock Purchase Plan, value			608,000		608,000
Common stock issued upon exercise of options, shares		312,893
Common stock issued upon exercise of options, value			298,000		298,000
Share-based compensation			6,702,000		6,702,000
Net loss				(50,358,000)	(50,358,000)
Ending balance, shares at Apr. 30, 2015	1,574,764	193,346,627
Ending balance, value at Apr. 30, 2015	$ 2,000	$ 193,000	512,464,000	(453,624,000)	59,035,000
Series E preferred stock issued for cash, net of issuance costs, shares	2,676
Series E preferred stock issued for cash, net of issuance costs, value			59,000		59,000
Series E preferred stock dividends			(4,139,000)		(4,139,000)
Common stock issued for cash, net of issuance costs, shares		42,372,195
Common stock issued for cash, net of issuance costs, value		$ 43,000	45,152,000		45,195,000
Common stock issued under Employee Stock Purchase Plan, shares		1,034,397
Common stock issued under Employee Stock Purchase Plan, value		$ 1,000	539,000		540,000
Common stock issued upon exercise of options, shares		177,266
Common stock issued upon exercise of options, value			138,000		138,000
Share-based compensation			4,898,000		4,898,000
Net loss				(55,652,000)	(55,652,000)
Ending balance, shares at Apr. 30, 2016	1,577,440	236,930,485
Ending balance, value at Apr. 30, 2016	$ 2,000	$ 237,000	$ 559,111,000	$ (509,276,000)	$ 50,074,000