Area of land subject to a ground lease.

No definition available.

Name:	us-gaap_LandSubjectToGroundLeases
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LesseeLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of terms and conditions of option to extend lessee's operating lease. Includes, but is not limited to, information about option recognized as part of right-of-use asset and lease liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseOptionToExtend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of operating lease expense. Excludes sublease income.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 4
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918638-209977

+ Details

Name:	us-gaap_OperatingLeaseExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementLocationAxis=kalv_GeneralAndAdministrativeExpensesAndResearchAndDevelopmentExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=stpr_MA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=stpr_UT
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Leases - Additional Information (Detail) $ in Millions	12 Months Ended
Leases - Additional Information (Detail) $ in Millions	Apr. 30, 2022 USD ($) ft²	Apr. 30, 2021 USD ($)	Apr. 30, 2020 USD ($)
General and Administrative Expenses and Research and Development Expenses [Member]
Lessee Lease Description [Line Items]
Rent expense \| $	$ 1.7	$ 0.9	$ 0.7
Massachusetts [Member]
Lessee Lease Description [Line Items]
Lease agreement square feet	8,300
United Kingdom [Member]
Lessee Lease Description [Line Items]
Lease agreement square feet	13,400
Lease description option to extend	option to terminate in April 2023. As of April 2022, the Company does not expect to exercise the option to terminate the lease.
Utah [Member]
Lessee Lease Description [Line Items]
Lease agreement square feet	6,200