10. Sale of Research and Development Assets (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Apr. 30, 2019	[1],[2],[3]	Jan. 31, 2019	[1],[2],[3]	Oct. 31, 2018	[1],[2],[3]	Jul. 31, 2018	[1],[2],[3]	Apr. 30, 2018	[1],[2],[3]	Jan. 31, 2018	[1],[2],[3]	Oct. 31, 2017	[1],[2],[3]	Jul. 31, 2017	[1],[2],[3]	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Gain on sale of research and development assets before income taxes																	$ 1,000	$ 8,000	$ 0
Income (loss) from discontinued operations, net of tax	$ 102		$ 0		$ 739		$ 0		$ 9,154		$ (2,076)		$ (4,323)		$ (4,005)		841	(1,250)	(29,552)
Discontinued Operations [Member] [Default Label]
License revenue																	0	25	0
Total operating expenses																	0	9,275	29,552
Other income																	125	0	0
Gain on sale of research and development assets before income taxes																	1,000	8,000	0
Income tax expense																	284	0	0
Income (loss) from discontinued operations, net of tax																	841	(1,250)	(29,552)
Discontinued Operations [Member] [Default Label] | Research and Development Expense [Member]
Total operating expenses																	0	6,782	27,992
Discontinued Operations [Member] [Default Label] | Selling, General and Administrative Expenses [Member]
Total operating expenses																	0	2,163	1,560
Discontinued Operations [Member] [Default Label] | Restructuring Charges [Member]
Total operating expenses																	$ 0	$ 330	$ 0

[1] For all periods presented, the operating results of our former research and development segment are reported as income (loss) from discontinued operations, net of tax (Note 1).

[2] Income from discontinued operations, net of tax, for the quarters ended October 31, 2018 and April 30, 2018 include a gain on sale of research and development assets before tax of $1,000 and $8,000, respectively (Note 10).

[3] On May 1, 2018, we adopted ASC 606 using the modified retrospective method applied to all contracts not completed as of May 1, 2018 (Note 2). Under the modified retrospective method, results for the reporting periods beginning on or after May 1, 2018 are presented in accordance with ASC 606, while prior period amounts are not adjusted and continue to be reported under the accounting standards that were in effect prior to May 1, 2018.