Employee Stock Purchase Plan, Number Of Shares Authorized, Annual Increase

No definition available.

Name:	cdlx_EmployeeStockPurchasePlanNumberOfSharesAuthorizedAnnualIncrease
Namespace Prefix:	cdlx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Performance Shares, Advertiser Billing Period

+ References

No definition available.

+ Details

Name:	cdlx_PerformanceSharesAdvertiserBillingPeriod
Namespace Prefix:	cdlx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Performance Shares, EBITDA Target Period

+ References

No definition available.

+ Details

Name:	cdlx_PerformanceSharesEBITDATargetPeriod
Namespace Prefix:	cdlx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Performance Shares, Minimum Growth Rate Period

+ References

No definition available.

+ Details

Name:	cdlx_PerformanceSharesMinimumGrowthRatePeriod
Namespace Prefix:	cdlx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Performance Shares, Stock Closing Price Period

+ References

No definition available.

+ Details

Name:	cdlx_PerformanceSharesStockClosingPricePeriod
Namespace Prefix:	cdlx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Performance Shares, Vesting Condition Period

+ References

No definition available.

+ Details

Name:	cdlx_PerformanceSharesVestingConditionPeriod
Namespace Prefix:	cdlx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Non-Option Equity Instruments, Performance Conditions

+ References

No definition available.

+ Details

Name:	cdlx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsPerformanceConditions
Namespace Prefix:	cdlx_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Share-Based Payment Arrangement, Number Of Vesting Tranches

+ References

No definition available.

+ Details

Name:	cdlx_ShareBasedPaymentArrangementNumberOfVestingTranches
Namespace Prefix:	cdlx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized, Annual Percentage Increase

+ References

No definition available.

+ Details

Name:	cdlx_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesAuthorizedAnnualPercentageIncrease
Namespace Prefix:	cdlx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Remaining For Available For Issuance

+ References

No definition available.

+ Details

Name:	cdlx_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesRemainingForAvailableForIssuance
Namespace Prefix:	cdlx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of increase in lease obligation from new lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4313-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

+ Details

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

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cost to be recognized for option under share-based payment arrangement.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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=121586364&loc=d3e3602-108585

+ Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

STOCK-BASED COMPENSATION - Narrative (Details) $ in Thousands		1 Months Ended				6 Months Ended
	Feb. 08, 2018 shares	Jul. 31, 2021 USD ($) tranche shares	Apr. 30, 2021 shares	Apr. 30, 2020 user shares	Apr. 30, 2019 user tranche shares	Jun. 30, 2021 USD ($) tranche shares	Jun. 30, 2020 USD ($)	Dec. 31, 2020 shares	Jan. 01, 2020 shares	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	1,875,000							1,222,316
Number of shares remaining available for issuance (in shares)	61,247
Number of shares authorized, annual increase						5.00%
Lease Obligation Incurred \| $						$ 400	$ 200
Award vesting period						4 years
Expiration period						10 years
Options vested in period, fair value \| $						$ 400
Compensation not yet recognized \| $						$ 100
Common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized						3 months 18 days
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)						565,000
Unvested PSU (in shares)						2,588,000		2,434,000
Compensation cost not yet recognized						2 years 10 months 9 days
Stock option expense \| $						$ 108,964
Restricted stock units \| Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)						444,438
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested PSU (in shares)			110,236	476,608	1,252,500
Share-Based Payment Arrangement, Number Of Vesting Tranches \| tranche					4	2
Performance Shares, Minimum Growth Rate Period					12 months
Performance Shares, Advertiser Billing Period					12 months
Performance Shares, EBITDA Target Period					12 months
Performance Shares, Stock Closing Price Period					30 days
Performance Shares, ARPU Vesting Condition Period			4 years	4 years
Performance Shares \| Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			12 months	12 months
Unvested PSU (in shares)			55,118	443,276
Share-Based Compensation Arrangement By Share-Based Payment Award, Non-Option Equity Instruments, Performance Conditions \| user				0.50	0.50
Performance Shares \| Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			6 months	6 months	6 months
Unvested PSU (in shares)			55,118	33,332
Share-Based Compensation Arrangement By Share-Based Payment Award, Non-Option Equity Instruments, Performance Conditions \| user				0.25	0.25
Performance Shares \| Share-based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				12 months	12 months
Share-Based Compensation Arrangement By Share-Based Payment Award, Non-Option Equity Instruments, Performance Conditions \| user				0.25	0.25
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized, annual increase										1.00%
ESPP, purchase price percentage	85.00%
ESPP, number of shares authorized, annual increase (in shares)						500,000		474,120,000	278,608,000
Common Stock Options From Dosh Acquisition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)						104,098
Options vested in period, fair value \| $						$ 1,100
Compensation not yet recognized \| $						$ 5,200
Compensation cost not yet recognized						2 years 6 months
Common Stock Options From Dosh Acquisition \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period						1 year
Common Stock Options From Dosh Acquisition \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period						4 years
Subsequent Event \| Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)		73,310
Compensation not yet recognized, awards other than options \| $		$ 13,200
Subsequent Event \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Payment Arrangement, Number Of Vesting Tranches \| tranche		2