FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Measurement Transfer Levels (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024	Dec. 31, 2023
FAIR VALUE OF FINANCIAL INSTRUMENTS
Transfer from level 1 to level 2, Assets	$ 0	$ 0
Transfer from level 2 to level 1, Assets	0	0
Transfer from level 1 to level 2, Liability	0	0
Transfer from level 2 to level 1, Liability	0	0
Transfer into level 3, Assets	0	0
Transfer out of level 3, Assets	0	0
Transfer into level 3, Liability	0	0
Transfer out of level 3, Liability	$ 0	$ 0

Amount of transfer of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of transfer of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

No definition available.

+ Details

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Namespace Prefix:	kala_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of transfer of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

No definition available.

+ Details

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Namespace Prefix:	kala_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of transfer of liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

No definition available.

+ Details

Name:	kala_FairValueLiabilitiesLevel2ToLevel1TransfersAmount1
Namespace Prefix:	kala_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Amount of transfers of financial instrument classified as a liability into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

+ References

+ Details

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

- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

+ Details

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

- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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