RELATED PARTIES - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
Feb. 28, 2018	Jun. 30, 2020
Related Party Transaction [Line Items]
Proceeds from Warrant Exercises		$ 15.2
Class of Warrant or Right, Exercised		644,365
Common Stock Warrants
Related Party Transaction [Line Items]
Stock option expense	$ 2.5

Class of Warrant or Right, Exercised

No definition available.

Name:	cdlx_ClassofWarrantorRightExercised
Namespace Prefix:	cdlx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with the amount received from holders exercising their stock warrants.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3255-108585

+ Details

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

- 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

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

- Definition

Amount of noncash expense for option under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

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

- Details

Name:	us-gaap_AwardTypeAxis=cdlx_CommonStockWarrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: