For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13531-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Revenue - Customer Concentration and Accounts Receivable (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020	Apr. 30, 2020
Disaggregation of Revenue [Line Items]
Unbilled receivables	$ 0.6		$ 0.6		$ 0.5
Customer Concentration Risk \| Revenue \| Customer One
Disaggregation of Revenue [Line Items]
Customer concentration risk, percentage	16.00%	24.00%	16.00%	27.00%
Customer Concentration Risk \| Revenue \| Customer Two
Disaggregation of Revenue [Line Items]
Customer concentration risk, percentage	12.00%	10.00%	12.00%	10.00%
Customer Concentration Risk \| Accounts Receivable \| Customer One
Disaggregation of Revenue [Line Items]
Customer concentration risk, percentage			21.00%		33.00%
Customer Concentration Risk \| Accounts Receivable \| Customer Two
Disaggregation of Revenue [Line Items]
Customer concentration risk, percentage			13.00%		19.00%
Customer Concentration Risk \| Accounts Receivable \| Customer Three
Disaggregation of Revenue [Line Items]
Customer concentration risk, percentage			11.00%		15.00%