Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2020	Jan. 31, 2019	May 01, 2019	Apr. 30, 2019
Accounting Policies [Abstract]
Net income	$ 407	$ 307	$ (641)	$ (369)	$ 267	$ 483	$ 72	$ 381
Net cash provided by (used in) operating activities							360	1,610
Accumulated deficit	70,625						70,625			$ 70,698
Working capital deficit	(300)						(300)
Cash and cash equivalents	3,282						3,282			3,237
Unrecognized tax benefits	151						151			$ 151
Provision for income taxes	12			$ 0			38	$ 0
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets, net	2,902						2,902
Present value of minimum payments due	$ 10,486						$ 10,486
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets, net									$ 3,200
Deferred rent									900
Operating lease liability									4,100
Present value of minimum payments due									$ 4,100