4. Stockholders' Equity (Details Narrative) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Preferred stock par value (in Dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	1,647,760	1,647,760
Preferred stock, shares outstanding	1,647,760	1,647,760
Dividends paid	$ 4,325	$ 4,325	$ 4,279
Proceeds from sale of common stock	0	25,687	30,450
Proceeds from sale of preferred stock	$ 0	0	1,576
Series E Preferred Stock [Member]
Preferred stock, shares authorized	2,000,000
Preferred stock, shares issued	1,647,760
Preferred stock, shares outstanding	1,647,760
Conversion price per share	$ 21.00
Redemption price	25.00
Liquidation preference price per share	$ 2.625
Dividends paid	$ 4,325	4,325	$ 4,279
Common stock to be issued if Series E stock is converted	1,961,619
Each outstanding share that could be converted into common shares	4.18
Series E Preferred Stock [Member] | AMI Sales Agreement [Member]
Stock issued new, shares			70,320
Proceeds from sale of preferred stock			$ 1,634
Common Stock
Payment of stock issuance costs		$ 1,780	$ 827
Common Stock | Public Offering [Member]
Stock issued new, shares		10,294,445
Proceeds from sale of common stock		$ 23,163
Payment of stock issuance costs		$ 1,669
Common Stock | AMI Sales Agreement [Member]
Stock issued new, shares		1,051,259	6,137,403
Proceeds from sale of common stock		$ 4,304	$ 18,246
Common Stock | Equity Distribution Agreement [Member]
Stock issued new, shares			3,750,323
Proceeds from sale of common stock			$ 13,031
Warrants [Member]
Warrants expired	39,040
Warrants issued	0
Warrants outstanding	0