10. SALE OF RESEARCH AND DEVELOPMENT ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Operating expenses:
Selling, general and administrative	$ 3,242	$ 4,824	$ 9,273	$ 12,273
Restructuring charges	0	0	0	1,258
Total operating expenses	3,242	4,824	9,273	13,531
Gain on sale of research and development assets before income taxes			1,000	0
Income tax expense (benefit)	44	0	217	0
Income (loss) from discontinued operations, net of tax	0	(2,076)	739	(10,404)
Discontinued Operations [Member]
Operating expenses:
Research and development	0	374	0	7,590
Selling, general and administrative	0	1,315	0	2,097
Restructuring charges	0	0	0	330
Total operating expenses	0	1,689	0	10,017
Other expense	0	387	0	387
Gain on sale of research and development assets before income taxes	0	0	1,000	0
Income tax expense (benefit)	0	0	(261)	0
Income (loss) from discontinued operations, net of tax	$ 0	$ (2,076)	$ 739	$ (10,404)