Cardlytics (CDLX) 10-K 5 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 28, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Cardlytics, Inc.
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Entity Central Index Key	1,666,071
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	false
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 222
Entity Common Stock, Shares Outstanding (in shares)		22,502,113

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 39,623	$ 21,262
Restricted cash	20,247	0
Accounts receivable, net	58,125	48,348
Other receivables	2,417	2,898
Prepaid expenses and other assets	3,956	2,121
Total current assets	124,368	74,629
Long-term assets:
Property and equipment, net	10,230	7,319
Intangible assets, net	370	528
Capitalized software development costs, net	1,625	433
Deferred FI implementation costs, net	15,877	13,625
Other long-term assets, net	1,293	4,224
Total assets	153,763	100,758
Current liabilities:
Accounts payable	2,099	1,554
Accrued liabilities:
Accrued compensation	5,936	4,638
Accrued expenses	4,388	4,615
FI Share liability	27,656	23,914
Consumer Incentive liability	11,476	7,242
Deferred billings	346	132
Current portion of long-term debt	21	44
Total current liabilities	51,922	42,139
Long-term liabilities:
Deferred liabilities	3,173	3,670
Long-term warrant liability	0	10,230
Long-term debt, net of current portion	46,693	56,968
Total liabilities	101,788	113,007
Commitments and contingencies (Note 13)
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	196,437
Stockholders’ (deficit) equity:
Common stock, $0.0001 par value—83,000 and 100,000 shares authorized and 3,439 and 22,466 shares issued and outstanding as of December 31, 2017 and December 31, 2018, respectively	7	0
Additional paid-in capital	371,463	58,693
Accumulated other comprehensive income	1,992	1,066
Accumulated deficit	(321,487)	(268,445)
Total stockholders’ (deficit) equity	51,975	(208,686)
Total liabilities and stockholders’ (deficit) equity	153,763	100,758
Series G’ Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	44,672
Series G Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	5,110
Series F/F-R Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	58,449
Series E/E-R Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	29,972
Series D/D-R Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	32,728
Series C/C-R Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	18,366
Series B/B-R Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	0	5,288
Series A/A-R Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock	$ 0	$ 1,852

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, par or stated value per share (in usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	100,000,000	83,000,000
Common stock, shares issued (in shares)	22,466,000	3,439,000
Common stock, shares outstanding (in shares)	22,466,000	3,439,000
Series G’ Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	5,339,000
Redeemable convertible preferred stock, shares issued (in shares)	0	1,296,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	1,296,000
Series G Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	1,385,000
Redeemable convertible preferred stock, shares issued (in shares)	0	346,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	346,000
Series F/F-R Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	5,000,000
Redeemable convertible preferred stock, shares issued (in shares)	0	1,199,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	1,199,000
Series E/E-R Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	7,400,000
Redeemable convertible preferred stock, shares issued (in shares)	0	795,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	795,000
Series D/D-R Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	5,787,000
Redeemable convertible preferred stock, shares issued (in shares)	0	1,396,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	1,396,000
Series C/C-R Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	6,032,000
Redeemable convertible preferred stock, shares issued (in shares)	0	1,508,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	1,508,000
Series B/B-R Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	9,596,000
Redeemable convertible preferred stock, shares issued (in shares)	0	2,247,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	2,247,000
Series A/A-R Stock
Redeemable convertible preferred stock, par value (in usd per share)	$ 0	$ 0.0001
Redeemable convertible preferred stock, shares authorized (in shares)	0	7,528,000
Redeemable convertible preferred stock, shares issued (in shares)	0	1,857,000
Redeemable convertible preferred stock, shares outstanding (in shares)	0	1,857,000

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 150,684	$ 130,365	$ 112,821
Costs and expenses:
FI Share and other third-party costs	85,371	73,247	66,285
Delivery costs	10,632	7,012	6,127
Sales and marketing expense	41,878	31,927	31,261
Research and development expense	16,210	12,150	13,902
General and administration expense	34,228	20,100	21,355
Depreciation and amortization expense	3,282	3,028	4,219
Termination of U.K. agreement expense	0	0	25,904
Total costs and expenses	191,601	147,464	169,053
Operating loss	(40,917)	(17,099)	(56,232)
Other (expense) income:
Interest expense, net	(3,264)	(8,239)	(6,170)
Change in fair value of warrant liabilities, net	(6,760)	(581)	(32)
Change in fair value of convertible promissory notes	0	(1,244)	(786)
Change in fair value of convertible promissory notes—related parties	0	6,213	(10,091)
Other (expense) income, net	(2,101)	1,309	(2,385)
Total other expense	(12,125)	(2,542)	(19,464)
Loss before income taxes	(53,042)	(19,641)	(75,696)
Income tax benefit	0	0	0
Net loss	(53,042)	(19,641)	(75,696)
Adjustments to the carrying value of redeemable convertible preferred stock	(157)	(5,743)	(982)
Net loss attributable to common stockholders	$ (53,199)	$ (25,384)	$ (76,678)
Net loss per share attributable to common stockholders, basic and diluted (in USD per share)	$ (2.79)	$ (7.86)	$ (32.48)
Weighted-average common shares outstanding, basic and diluted (in shares)	19,060	3,230	2,361

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (53,042)	$ (19,641)	$ (75,696)
Other comprehensive income (loss):
Foreign currency translation adjustments	926	(1,036)	1,519
Total comprehensive loss	$ (52,116)	$ (20,677)	$ (74,177)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ (DEFICIT) EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2015		2,135
Beginning balance at Dec. 31, 2015	$ (162,161)	$ 0	$ 10,364	$ 583	$ (173,108)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	44	43
Exercise of common stock options	$ 279		279
Stock-based compensation	3,447		3,447
Issuance of common stock warrants	961		961
Conversion to common stock (in shares)		412
Conversion to common stock	15,021		15,021
Conversion of preferred stock warrants to common stock warrants	777		777
Accretion of redeemable stock	(982)		(982)
Other comprehensive income (loss)	1,519			1,519
Net loss	(75,696)				(75,696)
Ending balance (in shares) at Dec. 31, 2016		2,590
Ending balance at Dec. 31, 2016	$ (216,835)	$ 0	29,867	2,102	(248,804)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	47	48
Exercise of common stock options	$ 230		230
Stock-based compensation	$ 5,147		5,147
Issuance of common stock (in shares)	1,296
Issuance of common stock warrants	$ 312		312
Deemed dividend related to beneficial conversion feature	(4,488)		(4,488)
Beneficial conversion feature of Series G stock	4,488		4,488
Conversion to common stock (in shares)		801
Conversion to common stock	24,392		24,392
Accretion of redeemable stock	(1,255)		(1,255)
Other comprehensive income (loss)	(1,036)			(1,036)
Net loss	(19,641)				(19,641)
Ending balance (in shares) at Dec. 31, 2017		3,439
Ending balance at Dec. 31, 2017	$ (208,686)	$ 0	58,693	1,066	(268,445)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	357	356
Exercise of common stock options	$ 1,959		1,959
Exercise of common stock warrants (in shares)		1,142
Stock-based compensation	26,813		26,813
Issuance of common stock (in shares)		5,821
Issuance of common stock	66,101	$ 1	66,100
Issuance of common stock warrants	17,774		17,774
Issuance of ESPP (in shares)		177
Issuance of ESPP	1,958		1,958
Settlement of restricted stock (in shares)		888
Conversion to common stock (in shares)		10,643
Conversion to common stock	196,594	$ 6	196,588
Conversion of preferred stock warrants to common stock warrants	1,735		1,735
Accretion of redeemable stock	(157)		(157)
Other comprehensive income (loss)	926			926
Net loss	(53,042)				(53,042)
Ending balance (in shares) at Dec. 31, 2018		22,466
Ending balance at Dec. 31, 2018	$ 51,975	$ 7	$ 371,463	$ 1,992	$ (321,487)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (53,042)	$ (19,641)	$ (75,696)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,282	3,028	4,219
Amortization of financing costs charged to interest expense	282	560	297
Accretion of debt discount and non-cash interest expense	2,326	6,889	4,368
Stock-based compensation	26,790	5,147	3,447
Termination of U.K. agreement expense	0	0	25,904
Change in the fair value of warrant liabilities, net	6,760	581	32
Change in the fair value of convertible promissory notes	0	1,244	786
Change in the fair value of convertible promissory notes - related parties	0	(6,213)	10,091
Other non-cash expense (income), net	4,771	(1,102)	6,219
Amortization and impairment of deferred FI implementation costs	1,618	1,626	1,690
Settlement of paid-in-kind interest	(8,353)	0	0
Change in operating assets and liabilities:
Accounts receivable	(9,426)	(7,503)	(5,789)
Prepaid expenses and other assets	(2,275)	(666)	(529)
Deferred FI implementation costs	(9,250)	(10,900)	(8,200)
Recovery of deferred FI implementation costs	5,380	4,100	0
Accounts payable	911	(1,907)	(1,234)
Other accrued expenses	3,255	466	(3,940)
Payable to related party, net	0	0	(459)
FI Share liability	3,742	804	8,482
Customer Incentive liability	4,234	1,385	(2,186)
Net cash used in operating activities	(18,995)	(22,102)	(32,498)
Investing activities
Acquisition of property and equipment	(5,920)	(1,215)	(1,827)
Acquisition of patents	(23)	(60)	(72)
Capitalized software development costs	(1,399)	(372)	(646)
Net cash used in investing activities	(7,342)	(1,647)	(2,545)
Financing activities
Proceeds from issuance of debt	47,435	12,500	46,794
Proceeds from issuance of debt—related parties	0	0	19,485
Principal payments of debt	(52,581)	(99)	(32,346)
Proceeds from issuance of common stock	72,334	230	279
Proceeds from issuance of Series G preferred stock	0	11,940	0
Equity issuance costs	(1,949)	(2,668)	(1,674)
Debt issuance costs	(48)	(142)	(1,417)
Debt extinguishment costs	0	0	(312)
Net cash from financing activities	65,191	21,761	30,809
Effect of exchange rates on cash, cash equivalents and restricted cash	(246)	282	(407)
Net (decrease) increase in cash, cash equivalents and restricted cash	38,608	(1,706)	(4,641)
Cash, cash equivalents, and restricted cash — Beginning of period	21,262	22,968	27,609
Cash, cash equivalents, and restricted cash — End of period	59,870	21,262	22,968
Supplemental schedule of non-cash investing and financing activities:
Amounts accrued for property and equipment	640	750	0
Amounts accrued for capitalized software development costs	$ 0	$ 61	$ 0

NATURE OF OPERATIONS

NATURE OF OPERATIONS	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF OPERATIONS	Cardlytics, Inc. (“we,” “our,” “us,” the “Company,” or “Cardlytics”) is a Delaware corporation and was formed on June 26, 2008. We make marketing more relevant and measurable through our purchase intelligence platform. Using one of the largest aggregations of purchase data through our partnerships with banks and credit unions, we have a secure view into where and when consumers are spending their money. By applying advanced analytics to this massive aggregation of anonymized purchase data, we make it actionable, helping marketers identify, reach and influence likely buyers at scale, and measure the true sales impact of their marketing spend. On May 4, 2012, we formed Cardlytics UK Limited (“Cardlytics UK”), a wholly-owned subsidiary registered as a private limited company in England and Wales. As discussed in Note 12—Variable Interest Entity, Cardlytics UK was a party to a collaboration agreement whereby 50% of its income and losses are shared with Aimia EMEA Limited (“Aimia”). Cardlytics, Inc. obtained full control of Cardlytics UK in June 2016 upon the termination of the cooperation agreement in exchange for convertible promissory notes of the Company. Refer to Note 5—Debt for additional information. Reverse Stock Split On January 26, 2018, our board of directors approved an amended and restated certificate of incorporation to (1) effect a reverse split on outstanding shares of our common stock and redeemable convertible preferred stock on a one-for-four basis (the “Reverse Stock Split”), (2) modify the threshold for automatic conversion of our preferred stock into shares of our common stock in connection with an initial public offering to eliminate the requirement of gross proceeds to the Company of not less than $70.0 million and (3) authorize us to issue up to 100,000,000 shares of common stock, $0.0001 par value per share and 25,000,000 shares of redeemable convertible preferred stock, $0.0001 par value per share (collectively, the “Charter Amendment”). The authorized shares and par values of our common stock and redeemable convertible preferred stock were not adjusted as a result of the Reverse Stock Split. The Charter Amendment was approved by the Company’s stockholders on January 26, 2018 and became effective upon the filing of the Charter Amendment with the State of Delaware on January 26, 2018. All issued and outstanding common stock and preferred stock and related share and per share amounts contained in these financial statements have been retroactively adjusted to reflect the Reverse Stock Split for all periods presented. Initial Public Offering On February 13, 2018 , we closed our initial public offering (“IPO”), in which we issued and sold 5,400,000 shares of common stock at a public offering price of $13.00 per share, resulting in gross proceeds of $70.2 million . On February 14, 2018, pursuant to the underwriters’ partial exercise of their over-allotment option to purchase up to an additional 810,000 shares from us, we issued and sold an additional 421,355 shares of our common stock, resulting in additional gross proceeds to us of $5.5 million . In total, we issued 5,821,355 shares of common stock and raised $75.7 million in gross proceeds, or $66.1 million in net proceeds after deducting underwriting discounts and commissions of $5.3 million and offering costs of $4.3 million . Upon the closing of the IPO, all of the outstanding shares of redeemable convertible preferred stock automatically converted into shares of common stock and all warrants to purchase shares of redeemable convertible preferred stock were automatically converted into warrants to purchase shares of common stock. Subsequent to the closing of the IPO, there were no shares of preferred stock or warrants to purchase shares of redeemable convertible preferred stock outstanding. The consolidated financial statements as of December 31, 2017, including share and per share amounts, do not give effect to the IPO or conversion of the redeemable convertible preferred stock, as the IPO and such conversions were completed subsequent to December 31, 2017 . Upon the completion of our IPO, our amended and restated certificate of incorporation authorized us to issue up to 100,000,000 shares of common stock, $0.0001 par value per share, and 10,000,000 shares of preferred stock, $0.0001 par value per share, all of which shares of preferred stock are undesignated. Our board of directors may establish the rights and preferences of the preferred stock from time to time.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements. Actual results could differ from these estimates. Significant items subject to such estimates and assumptions include revenue recognition, internal-use software development costs, income taxes, stock-based compensation, derivative instruments, income tax valuation allowance, contingencies and changes in fair value of our convertible promissory notes. We base our estimates on historical experience and also on assumptions that we believe are reasonable. Changes in facts or circumstances may cause us to change our assumptions and estimates in future periods and it is possible that actual results could differ from our current or revised future estimates. Foreign Currency The functional currency of our foreign wholly owned subsidiaries is the local currency. We translate the financial statements of these subsidiaries into U.S. dollars each reporting period for purposes of consolidation. Assets and liabilities are translated at the period-end currency exchange rates, certain equity accounts are translated at historical exchange rates and income and expense amounts are translated at average currency exchange rates in effect for the period. The effect of these translation adjustments is reported in a separate component of stockholders’ deficit titled accumulated other comprehensive income. We are also subject to gains and losses from foreign currency denominated transactions and the remeasurement of foreign currency denominated balance sheet accounts, both of which are included in other expense, net in the accompanying consolidated statements of operations. We recorded foreign currency losses (gains) totaling $1.9 million and $(1.3) million and $1.2 million in 2016 , 2017 and 2018 , respectively. Revenue We generate revenue through the sale of two categories of solutions that leverage our intelligence platform: (1) our proprietary native banking channel, Cardlytics Direct and (2) our Other Platform Solutions. We have generated substantially all of our revenue from sales of Cardlytics Direct since inception. Our Other Platform Solutions enabled marketers and marketing service providers to leverage the power of purchase intelligence outside the bank channel. We have shifted the majority of our efforts and resources to support the growth of Cardlytics Direct. As a result, we do not expect to generate substantial, if any, revenue from Other Platform Solutions for the foreseeable future. Cardlytics Direct Cardlytics Direct is our proprietary native bank advertising channel that enables marketers to reach consumers through their trusted and frequently visited online and mobile banking channels. Working with the marketer, we design a campaign that targets customers based on their purchase history. The consumer is offered an incentive to make a purchase from the marketer within a specified period. We use a portion of the fees that we collect from marketers to provide these consumer incentives to our FIs’ customers after they make qualifying purchases ("Consumer Incentives"). Leveraging our powerful predictive analytics, we are able to create compelling Consumer Incentives that have the potential to increase return on advertising spend for marketers. We also pay our FI partners an FI Share. Cardlytics Direct is priced predominantly in two ways: (1) Cost per Served Sale (“CPS”), and (2) Cost per Redemption (“CPR”). In 2016 , 2017 and 2018 , CPS represented 67% , 66% and 68% of our revenue from Cardlytics Direct. • CPS . Our primary pricing model is CPS, which we created to meet the media buying preferences of marketers. We generate revenue by charging a percentage, which we refer to as the CPS Rate, of all purchases from the marketer by consumers (1) who are served marketing and (2) subsequently make a purchase from the marketer during the campaign period, regardless of whether consumers select the marketing and thereby becomes eligible to earn the applicable Consumer Incentive. We set CPS Rates for marketers based on our expectation of the marketer’s return on spend for the relevant campaign. Additionally, we set the amount of the Consumer Incentives payable for each campaign based on our estimation of our ability to drive incremental sales for the marketer. We seek to optimize the level of Consumer Incentives to retain a greater portion of billings. However, if the amount of Consumer Incentives exceeds the amount of billings that we are paid by the applicable marketer we are still responsible for paying the total Consumer Incentive. This has occurred infrequently and has been immaterial in amount for each of the periods presented. • CPR . Our initial pricing model is CPR, where marketers specify and fund the Consumer Incentive and pay us a separate negotiated, fixed marketing fee, which we refer to as the CPR Fee, for each purchase that we generate. We generate revenue if the consumer (1) is served marketing, (2) selects the marketing and thereby becomes eligible to earn the applicable Consumer Incentive and (3) makes a qualifying purchase from the marketer during the campaign period. We set the CPR Fee for marketers based on our estimation of the marketers’ return on spend for the relevant campaign. The CPR Fee is either a percentage of qualifying purchases or a flat amount. Revenue Recognition We recognize revenue in accordance with Accounting Standards Codification (“ASC”) Topic 605, Revenue Recognition , on a transaction when all of the following conditions have been satisfied: • persuasive evidence of an agreement exists; • the service has been provided to the customer; • fees are fixed or determinable; and • the collection of the fees is reasonably assured. If any of these criteria are not met, revenue recognition is deferred until such time that all of the criteria are met. Our deferred revenue is primarily comprised of payments received in advance for Cardlytics Direct marketing campaigns. We sell our solutions by entering into agreements directly with marketers or their marketing agencies. The agreements state the terms of the arrangement, the agreed upon fee and, with respect to Cardlytics Direct, the fixed period of time the offers will be available to FI customers. Persuasive evidence of an arrangement is considered to exist and the fee is considered fixed and determinable upon the execution of an insertion order. With respect to our Cardlytics Direct service, the service is deemed to have been provided to the marketer as FIs’ customers make qualifying purchases during the marketing campaign term. With respect to Other Platform Solutions, the service is deemed to have been provided (1) for non-managed service campaigns, when we deliver the purchase intelligence to the marketer and (2) for managed service campaigns, when the digital advertising impressions contemplated by the campaign have been served to targeted consumers. We determine collectability upfront and on an on-going basis by performing credit evaluations and monitoring our marketers’ accounts receivable balances. Gross/Net Consideration We evaluate the appropriateness of revenue reporting on a gross or net basis by considering the indicators outlined within ASC Topic 605-45, Revenue Recognition—Principal Agent Considerations and ASC Topic 605-50, Customer Payments and Incentives . We consider the nature of the costs and risks associated with the indicators present in evaluating the substance of an arrangement. We consider the relative strength of each indicator and certain factors may be assessed to carry more weight in the evaluation. Consumer Incentives Cardlytics Direct is our proprietary native bank advertising channel that enables marketers to reach consumers via their trusted and frequently visited online and mobile banking channels as well as email. Working with the marketer, we design a campaign that targets customers based on their purchase history. The consumer is offered an incentive to make a purchase from the marketer within a specified period, which we refer to as Consumer Incentives. We use a portion of the fees that we collect from marketers to provide these Consumer Incentives to our FIs’ customers after they make qualifying purchases. We report our revenue on our consolidated statements of operations net of Consumer Incentives. We do not provide the goods or services that are purchased by our FIs’ customers from the marketers to which the Consumer Incentives relate. Accordingly, the marketer is deemed to be the principal in the relationship with the customer and, therefore, the Consumer Incentive is deemed to be a reduction in the purchase price paid by the customer for the marketer’s goods or services. While we are responsible for remitting Consumer Incentives to our FI partners for further payment to their customers, we function solely as an agent of marketers in these arrangements. Accounts receivable is recorded at the amount of gross billings to marketers, net of allowances, for the fees and Consumer Incentives that we are responsible to collect. Our accrued liabilities also include the amount of Consumer Incentives due to FI partners. As a result, accounts receivable and accrued liabilities may appear large in relation to revenue, which is reported on a net basis. During 2016 , 2017 and 2018 , Consumer Incentives totaled $57.0 million , $61.2 million and $68.3 million , respectively. FI Share and Other Third-Party Costs We report our revenue on our consolidated statements of operations gross of FI Share. FI Share is included in FI Share and other third-party costs in our consolidated statements of operations, rather than as a reduction of revenue, because we and not our FI partners act as the principal in our arrangements with marketers. We are responsible for the fulfillment and acceptability of the services purchased by marketers. We also have latitude in establishing the price of our services, have discretion in supplier selection and earn variable amounts. FI partners only supply consumer purchase data and digital marketing space and have no involvement in the marketing campaigns or contractual relationship with marketers. We incurred media costs in connection with the delivery of managed services with respect to our Other Platform Solutions. We reported our revenue on our consolidated statements of operations gross of media costs. Media costs were included in FI Share and other third-party costs in our consolidated statements of operations, rather than as a reduction of revenue, because we and not exchanges or digital publishers acted as the principal in our arrangements with marketers. FI Share and Other Third-Party Costs FI Share and other third-party costs consist primarily of the FI Share that we pay our FI partners, media and data costs, and through June 30, 2016, allocation of revenue in the U.K. to Aimia as discussed in Note 12—Variable Interest Entity. FI Share and other third-party costs also include the amortization and impairment of implementation costs incurred pursuant to our agreements with certain FI partners, any incremental costs due to FIs as part of FI Share commitments, as well as a non-cash expense related to the vesting of warrants issued to an FI partner that accelerated upon the consummation of our IPO. With respect to Cardlytics Direct, we pay FI Share based on the gross billings to marketers less any Consumer Incentives that we pay to our FI partners and certain third-party data costs. To the extent that we use a specific FI customer’s anonymized purchase data in the delivery of our Other Platform Solutions, we pay the applicable FI partner an FI Share calculated based on the relative contribution of the data provided by the FI partner to the overall delivery of the services. Delivery Costs Delivery costs consist primarily of personnel-related costs of our campaign, data operations and production support teams, including salaries, benefits, bonuses and payroll taxes, as well as stock-based compensation expense. Delivery costs also include hosting facility costs, internally developed and purchased or licensed software costs, outsourcing costs and professional services costs. Accounts Receivable Accounts receivable are carried at the original invoiced amount less an allowance for doubtful accounts, determined based on the probability of future collection. When we become aware of circumstances that may decrease the likelihood of collection, we record a specific allowance against amounts due, which reduces the receivable to the amount that we believe will be collected. For all other accounts receivable, we determine the adequacy of the allowance based on historical loss patterns, the number of days that billings are past due and an evaluation of the potential risk of loss associated with specific accounts. The following table presents changes in the allowance for doubtful accounts (in thousands): Year Ended December 31, 2016 2017 2018 Beginning balance $ 746 $ 653 $ 105 Bad debt expense 1,100 73 130 Write-offs, net of recoveries (1,193 ) (621 ) (66 ) Ending balance $ 653 $ 105 $ 169 Unbilled receivables were $0.5 million , $0.1 million and $0.4 million as of December 31, 2016 , 2017 and 2018 , respectively. An unbilled receivable represents revenue earned and recognized from customer activity that was not billed prior to the end of the reporting period. Unbilled receivables are included in accounts receivable, net on our consolidated balance sheets. Concentrations of Risk Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents and accounts receivable. Our cash and cash equivalents are held with three financial institutions, which we believe are of high credit quality. We believe that our accounts receivable credit risk exposure is limited as a result of being diversified among a large number of marketers segregated by both geography and industry. Historically, we have not experienced significant write-downs of our accounts receivable. No marketer represented a significant concentration of our accounts receivable as of December 31, 2017 or December 31, 2018 . No marketer accounted for over 10% of revenue during 2016 , 2017 or 2018 . Our business is substantially dependent on a limited number of FI partners. We require participation from our FI partners in Cardlytics Direct and access to their purchase data in order to offer our solutions to marketers and their agencies. We must have FI partners with a sufficient number of customers and levels of customer engagement to ensure that we have robust purchase data and marketing space to support a broad array of incentive programs for marketers. Our agreements with a substantial majority of our FI partners have terms of three to five years but are generally terminable by the FI partner on 90 days or less prior notice. If an FI partner terminates its agreement with us, we would lose that FI as a source of purchase data and digital banking customers. A new FI partner launched the Cardlytics Direct program in November 2018 and accounted for 17% of our aggregate FI Share during the fourth quarter of 2018. During 2016 , 2017 , 2018 and the fourth quarter of 2018 , our largest FI partner in the U.S. accounted for approximately 64% , 63% , 64% and 55% of FI Share, respectively. During 2016 , 2017 , 2018 and the fourth quarter of 2018 , an FI partner in the U.K. accounted for 10% , 12% , 9% and 8% of FI Share, respectively. No other FI partners accounted for over 10% of FI Share during 2016 , 2017 , 2018 or the fourth quarter of 2018. Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents consist of cash held in checking accounts, upon which we earn up to a 1.1% annual rate of interest as of December 31, 2018 . Restricted cash primarily represents deposits held in an account controlled by our lender as additional security for our payment obligations under our 2018 Term Loan, upon which we earn a 1.4% annual rate of interest as of December 31, 2018 . Refer to Note 5—Debt for additional information regarding our 2018 Term Loan. Cash, cash equivalents and restricted cash as presented on our consolidated statements of cash flows consists of the following (in thousands): December 31, 2016 2017 2018 Cash and cash equivalents $ 22,838 $ 21,262 $ 39,623 Restricted cash 130 — 20,247 Cash, cash equivalents and restricted cash $ 22,968 $ 21,262 $ 59,870 Property and Equipment Property and equipment are stated at cost. Expenditures for maintenance and repairs are expensed as incurred, while betterments that materially extend the life of an asset are capitalized. The cost of assets sold, retired or otherwise disposed of, and the related accumulated depreciation, are eliminated from the accounts and any resulting gain or loss is recognized. Depreciation of property and equipment is determined using the straight-line method over the estimated useful lives of the applicable assets, which are as follows: Computer equipment: 2–3 years Furniture and fixtures: 5 years Leasehold improvements: Lesser of estimated useful life or life of the lease Intangible Assets Intangible assets are recorded at cost and consist of costs incurred for software patent applications. We received approval for three patents in 2013 and one patent in 2018 and began amortizing the costs of obtaining these patents over the estimated remaining lives of the patents. If a patent application is rejected or if we abandon efforts to obtain a new patent, all deferred patent costs are expensed immediately. Deferred patent costs related to patents for which we have not yet obtained approval totaled $0.4 million and $0.2 million as of December 31, 2017 and 2018 , respectively. Based on deferred patent costs as of December 31, 2018 , the related amortization expense will be less than $0.1 million in each of the next five years. Intangible assets are as follows (in thousands): December 31, 2017 2018 Deferred patent costs, gross $ 563 $ 417 Less accumulated amortization (35 ) (47 ) Deferred patent costs, net $ 528 $ 370 Internal-Use Software Development Costs Capitalized software development costs consist of costs incurred in the development of internal-use software, primarily associated with the development and enhancement of our offer management system and offer placement system. We capitalize the costs of software developed or obtained for internal use in accordance with ASC Topic 350-40, Internal Use Software . We begin to capitalize our costs upon completion of the preliminary project stage. We consider the preliminary project stage to be complete and the application development stage to have begun when preliminary development efforts are successfully completed, management has authorized and committed project funding and it is probable that the project will be completed and the software will be used as intended. These costs are amortized on a straight-line basis over the estimated useful life of the related asset, generally estimated to be five years. Costs incurred in the preliminary project stage and post-implementation operation stages are expensed as incurred and recorded in research and development expense on our consolidated statements of operations. In 2016 , we suspended the development costs for new technology related to the delivery of our Other Platform Solutions as well as a new billing system and wrote off development costs totaling $1.2 million recognized in depreciation and amortization on our consolidated statement of operations. During 2017 and 2018 , we capitalized development costs for enhancements to our offer management system as well as the implementation of a new billing system totaling $0.4 million and $1.6 million , respectively. Capitalized software development costs are as follows (in thousands): December 31, 2017 2018 Capitalized software development costs, gross $ 1,487 $ 2,826 Less accumulated amortization (1,054 ) (1,201 ) Capitalized software development costs, net $ 433 $ 1,625 Impairment of Long-Lived Assets We review long-lived assets and intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be fully recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of the assets to the undiscounted future net cash flows expected to be generated by the assets. If such assets are not considered to be recoverable, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the fair value of the assets. During 2016 , we wrote off $0.8 million of deferred FI implementation costs as discussed in Note 13—Commitments and Contingencies. During 2017 and 2018 , no impairment of our long-lived assets and intangibles assets was recognized. Debt Issuance Costs Costs incurred to obtain loans, other than lines of credit, are recorded as a reduction of the carrying amount of the related liability and amortized over the applicable loans’ life using the effective interest method. Costs incurred to obtain lines of credit are capitalized and included in other long-term assets on our consolidated balance sheets and amortized ratably over the term of the arrangement. Costs incurred to obtain loans for which we have elected the fair value option are expensed upon the issuance of the loan and recorded within general and administrative expense on our consolidated statements of operations. As described in Note 5—Debt, we entered into a New Loan Facility in 2018 and deferred $0.1 million of debt issuance costs associated with obtaining the New Loan Facility and deferred $0.1 million of unamortized debt issuance costs attributed to our 2016 Line of Credit and 2016 Term Loan. We recognized a $0.9 million loss on extinguishment of debt related to the unamortized discount and unamortized debt issuance costs associated with our 2016 Term Loan and 2016 Line of Credit. This expense is included within other income, net on our consolidated statements of operations and is presented in other non-cash expenses on our consolidated statement of statement of cash flows. Amortization of debt issuance costs included in interest expense, net totaled $0.3 million , $0.6 million and $0.3 million in 2016 , 2017 and 2018 , respectively. In 2016, we also incurred $0.7 million of issuance costs, recorded in general and administrative expense, related to our convertible promissory notes, for which we have elected the fair value option. Deferred debt issuance costs related to our lines of credit included in other long-term assets are as follows (in thousands): December 31, 2017 2018 Debt issuance costs, gross $ 695 $ 334 Less accumulated amortization (366 ) (234 ) Debt issuance costs, net $ 329 $ 100 Deferred debt issuance costs related to our term loans included in debt are as follows (in thousands): December 31, 2017 2018 Debt issuance costs, gross $ 572 $ 30 Less accumulated amortization (246 ) (10 ) Debt issuance costs, net $ 326 $ 20 Future amortization of debt issuance costs is as follows (in thousands): Years Ending December 31, Amortization 2019 $ 89 2020 31 Total $ 120 Deferred Offering Costs Deferred offering costs consist of incremental costs directly attributable to equity offerings. Deferred offering costs are included in other long-term assets on our consolidated balance sheets. Upon completion of an offering, these amounts are offset against the proceeds of the offering. Year Ended December 31, 2016 2017 2018 Beginning balance $ 1,213 $ — $ 3,144 Deferred costs 715 3,144 1,135 Recognized against offering proceeds — — (4,279 ) Write-off of costs related to terminated equity offering $ (1,928 ) $ — $ — Ending balance $ — $ 3,144 $ — Reduction in Force In 2016, we announced a strategic shift to rebalance our resources and put us on a faster path to potential profitability. This workforce reduction plan resulted in $1.3 million of charges, consisting primarily of severance and medical benefits, recognized in 2016 when the extent of our action was determined and could be estimated. All severance and medical benefits were paid to former employees as of December 31, 2016. Additionally, vested stock options of affected employees were cancelled and re-granted with similar terms, but with exercise periods of up to two years, resulting in stock compensation expense of less than $0.1 million . The following table summarizes the allocation of expenses related to the reduction in force on the consolidated statements of operations (in thousands): Year Ended December 31, 2016 Delivery costs $ 93 Sales and marketing 396 Research and development 553 General and administration 249 Total reduction in force costs $ 1,291 Advertising We expense advertising costs as incurred. These costs are included in sales and marketing expense on our consolidated statements of operations. Advertising costs include direct marketing costs such as print advertisements, market research, direct mail, public relations and trade show expenses and totaled $0.9 million , $0.7 million and $0.9 million in 2016 , 2017 and 2018 , respectively. Research and Development Costs Research and development expense consists primarily of personnel costs of our information technology ("IT") engineering, IT architecture and product development teams, including salaries, benefits, bonuses, stock-based compensation and payroll taxes. Research and development expense also includes outsourcing costs, software licensing costs, professional fees and travel expenses. Stock-Based Compensation We measure and recognize compensation expense for all stock options and restricted stock units based on the fair value of the award on the grant date. We use the Black-Scholes option pricing model to estimate the fair value of stock option awards. The fair value of RSUs is determined based on the value of the underlying common stock on the grant date. The fair value is recognized as expense over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis when the only condition to vesting is continued service. Forfeitures are accounted for when they occur. We recognize the fair value of stock options which contain performance conditions based upon the probability of the performance conditions being met. We have not issued awards where vesting is subject to a market condition; however, if we were to grant such awards in the future, recognition would be based on the derived service period. Expense for awards with performance conditions are estimated and adjusted on a quarterly basis based upon our assessment of the probability that the performance condition will be met. Refer to Note 6—Stock-based Compensation for additional information regarding our specific award plans and estimates and assumptions used to determine fair value. Redeemable Convertible Preferred Stock Warrant Liability Warrants to purchase shares of our redeemable convertible preferred stock are accounted for as derivative liabilities in accordance with ASC Topic 815, Derivatives and Hedging due to the terms of the warrants and related agreements. We have determined that these warrants do not meet the scope exception of a contract indexed to our stock because of fair value protections contained in agreements governing our redeemable convertible preferred stock as described in Note 8—Redeemable Convertible Preferred Stock. We record preferred stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses on our statements of operations. Upon the consummation of our IPO, all of the outstanding warrants to purchase shares of redeemable convertible preferred stock were automatically converted into warrants to purchase shares of common stock. Refer to Note 10—Fair Value Measurement for additional information . Common Stock Warrant Liability In connection with the Series G Stock financing, we issued warrants to purchase shares of our common stock that are accounted for as liabilities in accordance with ASC Topic 480, Distinguishing Liabilities From Equity due to the terms of the warrants and related agreements. We record these common stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses in our statements of operations. Refer to Note 10—Fair Value Measurement for additional information . Fair Value of Financial Instruments When required by GAAP, assets and liabilities are reported at fair value on our consolidated financial statements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Valuation inputs are arranged in a hierarchy that consists of the following levels: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. • Level 2 inputs are inputs other than Level 1 inputs such as quoted prices for similar assets or liabilities; quoted prices in markets with insufficient volume or infrequent transactions (less active markets); or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3 inputs are unobservable inputs for the asset or liability. Our nonfinancial assets that we recognize or disclose at fair value on our consolidated financial statements on a nonrecurring basis include property and equipment, intangible assets, capitalized software development costs and deferred FI implementation costs. The fair values for these assets are evaluated when events or changes in circumstances indicate the carrying value may not be recoverable. Preferred Stock Warrants Outstanding warrants to purchase shares of our redeemable convertible preferred stock are accounted for as derivative liabilities in accordance with ASC Topic 815, Derivatives and Hedging (“ASC 815”) due to the terms of the warrants and related agreements. We have determined that these warrants do not meet the scope exception of a contract indexed to our stock because of fair value protections contained in agreements governing our redeemable convertible preferred stock. We record preferred stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses on our consolidated statements of operations. Upon the consummation of our IPO, all warrants to purchase shares of our redeemable convertible preferred stock were converted to warrants to purchase shares of our common stock. Refer to Note 10—Fair Value Measurement for additional information regarding the valuation of warrants to purchase shares of our redeemable convertible preferred stock. Common Stock Warrants Issued in Connection with the Series G Stock Financing In connection with the Series G Stock financing, we issued warrants to purchase shares of our common stock that are accounted for as liabilities in accordance with ASC Topic 480, Distinguishing Liabilities From Equity due to the terms of the warrants and related agreements. We record these common stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses on our consolidated statements of operations. In August 2018, we issued warrants to purchase 792,434 shares of common stock at an exercise price of $0.0004 per share to the cash investors of our Series G financing, pursuant to our Series G stock purchase agreement. The warrants had a valuation of $15.3 million upon issuance and were subsequently exercised, resulting in the

ACCOUNTING STANDARDS

ACCOUNTING STANDARDS	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
ACCOUNTING STANDARDS	ACCOUNTING STANDARDS Recently Adopted Accounting Pronouncements In May 2017, the FASB issued ASU 2017-09, Scope of Modification Accounting , which amends the scope of modification accounting for share-based payment arrangements, provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under ASC Topic 718, Compensation—Stock Compensation . For all entities, the ASU is effective prospectively for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We adopted this ASU on January 1, 2018 and it did not have an impact on our consolidated financial statements. Recently Issued Accounting Pronouncements In May 2014, the FASB issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606). ASU 2014-09 supersedes the recognition guidance in ASC Topic 605 and most industry specific revenue guidance and requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which it expects to be entitled in exchange for those goods or services. In addition, this ASU requires disclosures of the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. This guidance permits the use of either the retrospective or modified retrospective transition method. For public entities, this ASU is effective for fiscal years beginning after December 15, 2017, including interim periods within those annual periods. For non-public entities, this ASU is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. We have made the election to use the extended transition period for complying with new or revised accounting standards under Section 102(b)(1) of the Jumpstart Our Business Startups Act of 2012 ("JOBS Act"), therefore we will be required to apply this ASU for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. We adopted this guidance on January 1, 2019 using the modified retrospective approach. We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which is intended to enhance the reporting model for financial instruments to provide users of financial statements with more decision-useful information. This ASU requires equity investments to be measured at fair value with changes in fair values recognized in net earnings, (public entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes), simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment and eliminates the requirement to disclose fair values, the methods and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost. This ASU also clarifies that management should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale debt securities in combination with other deferred tax assets. For public business entities, this ASU is effective for fiscal years beginning after December 15, 2017, including interim periods within those annual periods. For non-public business entities, this ASU is effective for fiscal years beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. Early adoption is permitted. We have made the election to use the extended transition period for complying with new or revised accounting standards under Section 102(b)(1) of the JOBS Act, therefore we will be required to apply this ASU for annual reporting periods beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. We adopted this guidance on January 1, 2019. We do not expect the adoption of this ASU to have a material impact on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , which supersedes ASC Topic 840, Leases . The ASU does not significantly change the lessees’ recognition, measurement and presentation of expenses and cash flows from the previous accounting standard. The ASU’s primary change is the requirement for lessee entities to recognize a lease liability for payments and a right of use asset representing the right to use the leased asset during the term on operating lease arrangements. Lessees are permitted to make an accounting policy election to not recognize the asset and liability for leases with a term of twelve months or less. Lessors’ accounting under the ASU is largely unchanged from the previous accounting standard. In addition, the ASU expands the disclosure requirements of lease arrangements. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842) - Targeted Improvements , which provides the option of applying the requirements of the new lease standard in the period of adoption with no restatement to comparative periods. For public entities, this ASU is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. For non-public entities, this ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We have made the election to use the extended transition period for complying with new or revised accounting standards under Section 102(b)(1) of the JOBS Act, therefore we will be required to adopt this ASU for annual reporting periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Although we are currently evaluating the impact of this guidance on our consolidated financial statements, we expect that most of our operating lease commitments will be recognized as operating lease liabilities and right-of-use assets upon adoption of the new guidance.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Significant components of property and equipment are as follows (in thousands): December 31, 2017 2018 Computer equipment $ 10,827 $ 16,284 Leasehold improvements 5,399 5,573 Furniture and fixtures 824 913 Construction in progress — 65 Property and equipment, gross 17,050 22,835 Less accumulated depreciation (9,731 ) (12,605 ) Property and equipment, net $ 7,319 $ 10,230 Assets acquired under capital leases, included within computer equipment, are as follows (in thousands): December 31, 2017 2018 Capital lease assets, gross $ 1,096 $ 1,096 Less accumulated depreciation (1,022 ) (1,047 ) Capital lease assets, net $ 74 $ 49 Depreciation expense was $3.0 million , $3.0 million and $3.0 million in 2016 , 2017 and 2018 , respectively.

DEBT

DEBT	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Our debt consists of the following (in thousands): December 31, 2017 2018 Lines of credit $ 25,081 $ 26,677 Term loans (1) 31,830 19,980 Capital leases 101 57 Total debt 57,012 46,714 Less current portion of long-term debt (44 ) (21 ) Long-term debt, net of current portion $ 56,968 $ 46,693 (1) Net of unamortized discount and debt issuance costs of $1,058 and $20 as of December 31, 2017 and 2018 , respectively. Accrued interest included in debt totaled $6.2 million and zero as of December 31, 2017 and 2018 , respectively. Paid-in-kind interest related to the convertible promissory notes is recognized in interest expense, net on our consolidated statements of operations and totaled $2.9 million and $1.7 million during 2016 and 2017 , respectively. Interest payments during 2016 , 2017 and 2018 totaled $1.6 million , $0.9 million and $9.7 million , respectively. New Loan Facility On May 21, 2018, we entered into a New Loan Facility consisting of a $30.0 million asset-based revolving line of credit ("2018 Line of Credit") and a $20.0 million term loan ("2018 Term Loan") maturing on May 21, 2020. We used the entire $20.0 million in proceeds from the 2018 Term Loan and an advance of $ 27.4 million under the 2018 Line of Credit to repay all outstanding obligations under our 2016 Line of Credit and 2016 Term Loan. Upon repayment, both the 2016 Line of Credit and the 2016 Term Loan were terminated. We deferred $0.1 million of debt issuance costs associated with obtaining the New Loan Facility and deferred $0.1 million of unamortized debt issuance costs attributed to our 2016 Line of Credit and 2016 Term Loan. Under the terms of the New Loan Facility relating to the 2018 Line of Credit, we are able to borrow up to the lesser of $30.0 million or 85% of the amount of our eligible accounts receivable. Interest on advances under the 2018 Line of Credit varies depending on the amount of unrestricted cash deposits we maintain with the lender on the last day of the month. The interest rate is equal to the prime rate minus 0.75% if our unrestricted deposits exceed $40.0 million , the prime rate minus 0.50% if our unrestricted deposits are between $40.0 million and $20.0 million , and the prime rate if our unrestricted deposits are below $20.0 million . As of December 31, 2018 , the indicative rate for advances on the 2018 Line of Credit was the prime rate minus 0.75% , or 4.75% . In addition, we are required to pay an unused line fee of 0.15% per annum on the average daily unused amount of the $30.0 million revolving commitment. We are also required to pay the lender a one-time success fee of $75,000 in the event that we achieve trailing twelve month revenue of $200.0 million or more at the end of any month after the closing date of the New Loan Facility. Interest accrues on the 2018 Term Loan at an annual rate of interest equal to the prime rate minus 2.75% , or 2.75% as of December 31, 2018 . All of our obligations under the New Loan Facility are also secured by a first priority lien on substantially all of our assets. Under the terms of the New Loan Facility, we are required to maintain a deposit of $20.0 million in a blocked account in favor of the lender as additional security for our payment obligations. The New Loan Facility contains a moving minimum trailing twelve month revenue covenant, which was $134.5 million for the period ended December 31, 2018 . The New Loan Facility also requires us to maintain a total cash balance plus liquidity under the 2018 Line of Credit of not less than $5.0 million . The New Loan Facility includes customary representations, warranties and covenants (affirmative and negative), including restrictive covenants that include restrictions on mergers, acquisitions and dispositions of assets, incurrence of indebtedness and encumbrances on our assets and a prohibition from the payment or declaration of dividends; in each case subject to specified exceptions. The New Loan Facility also includes standard events of default, including in the event of a material adverse change. Upon the occurrence of an event of default, the lender may declare all outstanding obligations immediately due and payable and take such other actions as are set forth in the New Loan Facility and increase the interest rate otherwise applicable to the 2018 Term Loan or advances under the 2018 Line of Credit by an additional 3.00% . In August 2018 and December 2018, we repaid $0.7 million and $0.1 million , respectively, of the outstanding balance under our 2018 Line of Credit. As of December 31, 2018 , we had $3.3 million of unused available borrowings under our 2018 Line of Credit. We were in compliance with all financial covenants as of December 31, 2018 . We expect to refinance or obtain a similar loan facility prior to its maturity date. In the event we are unable to refinance or obtain a similar loan facility under acceptable terms, we would repay our 2018 Line of Credit and 2018 Term Loan at or before its maturity. 2016 Line of Credit In September 2016, we entered into a $50.0 million loan and security agreement ("2016 Line of Credit") maturing on March 14, 2019. The 2016 Line of Credit facility was repaid and terminated in May 2018 in connection with obtaining our New Loan Facility. We recognized a $0.1 million loss on extinguishment of debt related to the unamortized debt issuance costs. This expense is included within other income, net in our consolidated statements of operations and is presented in other non-cash expenses on our consolidated statement of statement of cash flows. 2016 Term Loan In July 2016, we entered into a $24.0 million credit agreement ("2016 Term Loan") maturing on July 21, 2019. The 2016 Term Loan was repaid and terminated in May 2018 in connection with obtaining our New Loan Facility. We recognized a $0.8 million loss on extinguishment of debt related to the unamortized discount and unamortized debt issuance costs. This expense is included within other income, net in our consolidated statements of operations and is presented in other non-cash expenses on our consolidated statement of statement of cash flows. Convertible Promissory Notes Existing Stockholder Notes During 2016, we issued unsecured convertible promissory notes with an aggregate principal amount of $50.7 million . In May 2017, we issued and sold shares of Series G redeemable convertible preferred stock, which resulted in the conversion of the convertible promissory notes into either shares of our common stock or shares of our Series G’ Stock. Refer to Note 8—Redeemable Convertible Preferred Stock for additional information of the Series G Stock financing that resulted in the conversion of the convertible promissory notes. The redemption features included in the terms of the convertible promissory notes were determined to be derivative liabilities as a result of a significant discount within the redemption features for the note holders. Embedded derivatives that are not clearly and closely related to the host contract are required to be bifurcated and recorded at fair value unless the fair value option is elected on the host contract. Under the fair value option, bifurcation of the embedded derivative is not necessary as all related gains (losses) on the host contract and derivative will be reflected in the consolidated statements of operations. We elected the fair value option for the convertible promissory notes and recognized losses from their initial measurement during the second and third quarters of 2016. Subsequent changes in fair value of the convertible promissory notes are included in change in fair value of convertible promissory notes on our consolidated statements of operations. Refer to Note 10—Fair Value Measurement for additional information regarding the valuation of the convertible promissory notes. Aimia Notes During 2016, we issued to Aimia unsecured convertible promissory notes (“Aimia EMEA Notes”), in an aggregate principal amount of $18.0 million , which accrue interest at a rate of 10% per year, compounded annually. In consideration for our outstanding obligations to Aimia Inc. at the time we terminated our U.K. cooperation agreement, we issued to Aimia an unsecured convertible promissory note (“Outstanding Obligation Note”) in an aggregate principal amount of approximately $5.7 million , at an interest rate of 10% per year, compounded annually. Both the Aimia EMEA Notes and the Outstanding Obligation Note, (collectively the “Aimia Notes”) are due and payable on the earliest to occur of: (a) a date after June 30, 2019, as specified by the holder, (b) our liquidation, dissolution or wind up, including a sale of all or substantially all of our assets or a majority of our voting power or (c) an event of default. The Aimia Notes are subordinate to our Term Loan and Line of Credit. Refer to Note 11—Related Parties for additional information of the termination of the cooperation agreement with Aimia. The Aimia Notes were convertible into shares of our capital stock, depending on certain triggering events. In the event we completed an equity financing in which we received proceeds in excess of $10.0 million , the Aimia EMEA Notes were to automatically convert into shares of our common stock, at a price per share equal to 80% of the price per share determined by an independent third party valuation firm and the Outstanding Obligation Note was to automatically convert into shares of the same series of our capital stock as the investors in the financing, at a price per share equal to 80% of the price per share paid by such investors. In connection with the Series G Stock financing, the Aimia EMEA Notes converted into 801,329 shares of common stock. Refer to Note 8—Redeemable Convertible Preferred Stock for additional information of the Series G Stock financing and the transactions that resulted in the conversion of the Aimia EMEA Notes into shares of our common stock and the conversion of the Outstanding Obligation Note into shares of our Series G’ Stock. The redemption features included in the terms of the convertible promissory notes were determined to be derivative liabilities as a result of a significant discount within the redemption features for the note holders. Embedded derivatives that are not clearly and closely related to the host contract are required to be bifurcated and recorded at fair value unless the fair value option is elected on the host contract. Under the fair value option, bifurcation of the embedded derivative is not necessary as all related gains (losses) on the host contract and derivative will be reflected in the consolidated statements of operations. We elected the fair value option for the Existing Stockholder Notes and Aimia Notes and recognized losses from their initial measurement. Initial losses of $7.6 million related to the Existing Stockholder Notes is recorded in change in fair value of convertible promissory notes and the initial loss of $7.9 million related to the Aimia Notes is recorded in termination of U.K. agreement expense on our consolidated statements of operations. Subsequent changes in fair value of the Existing Stockholder Notes and Aimia Notes are included in change in fair value of convertible promissory notes on our consolidated statements of operations. Refer to Note 10—Fair Value Measurement for additional information . Working Capital Line of Credit We were party to a working capital line of credit with Aimia with maximum borrowings of £3.0 million (the “Working Capital Line of Credit”). The interest rate for borrowings under the Working Capital Line of Credit was equal to the 3-month LIBOR rate plus 5.25% . The Working Capital Line of Credit was secured by funds in a merchant bank account of Cardlytics UK and could only be used in the event that there was insufficient funds within the merchant account to fund Consumer Incentives in the U.K. The borrowings require repayment as customer payments were received by Cardlytics UK. The termination of the co-cooperation agreement also resulted in a termination of this Working Capital Line of Credit. Refer to Note 11—Related Parties for additional information regarding the related party relationship between Aimia and Cardlytics. Capital Leases We took delivery of leased computer equipment with minimum capital lease obligations of less than $0.1 million in 2016 and zero in 2017 and 2018 . Effective interest rates for equipment capital leases range from 0% to 13.3% . Fixed monthly payments for equipment under capital leases will be made through June 2021. Future Payments Aggregate future payments of principal and interest due upon maturity are as follows (in thousands): Years Ending December 31, Debt Capital leases Total debt 2019 $ — $ 20 $ 20 2020 46,677 24 46,701 2021 — 13 13 Total principal payments 46,677 57 46,734 Less unamortized debt issuance costs (20 ) — (20 ) Total debt $ 46,657 $ 57 $ 46,714

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION In May 2017, our board of directors and stockholders approved an increase in the total number of shares of common stock issuable under our 2008 Stock Plan ("2008 Plan") from 3,120,000 to 3,495,000 shares. In January 2018, our board of directors and stockholders approved an increase in the total number of shares of common stock issuable under our 2008 Plan to 4,020,000 shares. Our board of directors has adopted and our stockholders have approved our 2018 Equity Incentive Plan ("2018 Plan"). Our 2018 Plan became effective on February 8, 2018, the date our registration statement in connection with our IPO was declared effective. We do not expect to grant any additional awards under the 2008 Stock Plan. Any awards granted under the 2008 Plan will remain subject to the terms of our 2008 Plan and applicable award agreements. Initially, the aggregate number of shares of our common stock that may be issued pursuant to stock awards under the 2018 Plan is the sum of (i) 1,875,000 shares plus (ii) 61,247 shares reserved, and remaining available for issuance, under our 2008 Plan at the time our 2018 Plan became effective and (iii) the number of shares subject to stock options or other stock awards granted under our 2008 Plan that would have otherwise returned to our 2008 Plan (such as upon the expiration or termination of a stock award prior to vesting). The number of shares of our common stock reserved for issuance under our 2018 Plan will automatically increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2028, by 5% of the total number of shares of our capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by our board of directors. Accordingly, the number of shares of our common stock reserved for issuance under our 2018 Plan increased by 1,123,312 shares on January 1, 2019. The 2018 Plan provides for the grant of stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance-based stock awards and other forms of equity compensation, which are collectively referred to as stock awards. Additionally, the 2018 Plan provides for the grant of performance cash awards. The following table summarizes the allocation of stock-based compensation on the consolidated statements of operations (in thousands): Year Ended December 31, 2016 2017 2018 Delivery costs $ 96 $ 202 $ 633 Sales and marketing expense 1,153 1,894 9,358 Research and development expense 574 951 4,087 General and administration expense 1,624 2,100 12,712 Total stock-based compensation expense $ 3,447 $ 5,147 $ 26,790 During 2018 , we capitalized less than $0.1 million of stock-based compensation expense for software development. Common Stock Options The term of each option to purchase shares of our common stock pursuant to the Stock Plan is set by our board of directors or a committee thereof. Option awards are generally granted with an exercise price not less than the fair value per share of our common stock at the grant date. Option awards generally vest over four years and expire 10 years following the date of grant. We determine the grant date fair value of options using the Black-Scholes option pricing model, which is affected by the estimated fair value of our common stock as well as the following significant inputs: Year Ended December 31, 2016 2017 2018 Weighted-average grant date fair value $7.00 $12.11 $10.00 Significant inputs: Value of common stock $17.84 - $22.68 $24.60 - $28.16 $24.24 Expected term 7.0 years 7.0 years 7.0 years Volatility 51% to 56% 50% to 51% 50% Risk-free interest rate 0.5% - 2.1% 0.7% - 2.2% 2.7% We determined that a retrospective valuation of the fair value of our common stock on each grant date in 2016 was appropriate for financial reporting purposes. In connection with the preparation of our retrospective valuation, we noted that the fair value of our common stock, as determined by contemporaneous third-party valuations, decreased from $19.72 per share on April 30, 2016 to $17.84 per share on September 30, 2016. The decrease in the fair value of our common stock primarily resulted from the dilutive effect of issuing our convertible promissory notes as the Company’s enterprise values on April 30, 2016 and September 30, 2016 were similar and there were no events, or series of events, other than the issuance of the convertible promissory notes, which would have clearly resulted in a decrease in the fair value of our common stock. We derived the fair value of our common stock on each grant date between April 30, 2016 and September 30, 2016 using an interpolation methodology that considered both the timing and amount of dilution from issuing convertible promissory notes. For awards granted during the fourth quarter of 2016, we applied a straight-line calculation between the $17.84 per share price on September 30, 2016 to the $24.48 per share price on December 31, 2016. Using the benefit of hindsight, we determined that the straight-line calculation would provide the most appropriate conclusion for the valuation of our common stock on the interim dates between valuations because we did not identify any single event, or series of events, that occurred during this interim period that would have caused a material change in fair value other than our progress towards an IPO. We determined that a retrospective valuation of the fair value of our common stock on each grant date in 2017 was appropriate for financial reporting purposes. In connection with the preparation of our retrospective valuation, we noted that the fair value of our common stock, as determined by contemporaneous third-party valuations, was $24.48 per share on December 31, 2016, $27.68 per share on February 28, 2017, $30.44 per share on May 15, 2017 and $24.24 per share on September 30, 2017. The changes in fair value of our common stock primarily resulted from the dilutive effect of our Series G Stock financing, the timing of future potential liquidity events, changes to our forecasted financial results and changes in the valuation of comparable companies. We derived the fair value of our common stock on December 31, 2017 using a similar interpolation methodology and determined the fair value of our common stock to be $26.74 per share. A summary of common stock option activity is as follows (in thousands, except per share amounts): Shares Weighted-Average Exercise Price Per Share Options Outstanding - December 31, 2015 1,676 $ 11.04 Granted 1,330 18.08 Exercised (44 ) 6.00 Forfeited (685 ) 12.50 Cancelled (140 ) 11.82 Options Outstanding - December 31, 2016 2,137 15.00 Granted 799 23.78 Exercised (47 ) 4.83 Forfeited (159 ) 18.24 Cancelled (216 ) 7.54 Options Outstanding - December 31, 2017 2,514 18.42 Granted 29 24.24 Exercised (357 ) 6.25 Forfeited (197 ) 24.10 Cancelled (215 ) 16.60 Options Outstanding - December 31, 2018 1,774 $ 20.55 The total fair value of options vested during 2016 , 2017 and 2018 was approximately $2.9 million , $4.3 million and $6.0 million , respectively. As of December 31, 2018 , $6.3 million of unrecognized compensation expense related to unvested options will be recognized over a weighted-average period of 2.0 years. Restricted Stock Units A summary of restricted stock unit activity is as follows (in thousands, except per share amounts): Shares Weighted-Average Grant Date Fair Value Per Share Restricted Stock Units Outstanding - December 31, 2017 — $ — Granted 1,309 20.58 Vested (850 ) 21.93 Forfeited (78 ) 17.97 Restricted Stock Units Outstanding - December 31, 2018 381 $ 18.11 During the first quarter of 2018, we granted two separate tranches of performance-based restricted stock units ("2018 PSUs"), each to receive 437,500 shares of common stock, to employees. The vesting of the 875,000 2018 PSUs was contingent upon the completion of our IPO and includes other performance-based conditions. The performance condition in the first tranche will be satisfied if we attain 70.0 million of FI monthly active users ("FI MAUs") within three years of the grant date. The performance condition in the second tranche will be satisfied if we attain 85.0 million of average FI MAUs within five years of the grant date. FI MAUs is a performance metric defined within "Management's Discussion and Analysis of Financial Condition and Results of Operations." We recognize stock compensation for these 2018 PSUs based upon the expected timing of the achievement of these FI MAU targets. During 2018, 25,000 of the 2018 PSUs were forfeited prior to the FI MAU targets being reached. During the fourth quarter of 2018 , both average FI MAU targets were reached, resulting in the vesting of both tranches of the 2018 PSUs and the issuance of 850,000 shares of our common stock to fully settle the 2018 PSUs. During 2018, we recognized $18.6 million of stock-based compensation expense related to these awards. There is no unamortized stock-based compensation expense related to the 2018 PSUs as of December 31, 2018 . During 2018, we granted 434,377 restricted stock units ("RSUs") to employees and our non-employee directors, which have annual vesting periods ranging from one to four years. As of December 31, 2018 , there was approximately $4.5 million of unrecognized compensation expense related to RSUs, which is expected to be recognized over a weighted-average period of 2.4 years. Subsequent to December 31, 2018 , we granted 100,570 RSUs to employees, which have annual vesting periods ranging from two to four years. The unamortized stock-based compensation expense related to these RSUs is $1.8 million . Restricted Securities Units During 2016, we granted $1.0 million of restricted securities units to certain executives in lieu of cash bonuses. Upon issuance, the restricted securities units were indexed to the convertible promissory notes. As a result of the Series G Stock financing, the restricted securities units became indexed to our Series G’ Stock upon conversion of the convertible promissory notes. Upon the consummation of our IPO in February 2018, the restricted securities units became indexed to our common stock. Vesting requirements include both a service-based condition and a performance-based condition. The service-based condition requires each recipient to remain employed until the earlier of i) the date 6 months from the restricted securities unit grant date, ii) the date of a qualified liquidity event, or iii) date of termination without cause. The performance-based condition requires a sale of the Company or IPO event within a fixed period of time not more than 5 years from the restricted securities units grant date. The restricted securities units are considered liability classified awards, but due to the performance condition relating to sale of the Company or IPO, no compensation cost was recognized until one of these events occurred. These units vested upon the consummation of our IPO in February 2018, resulting in a non-cash expense of $0.5 million , and were settled upon the delivery of 37,406 shares of our common stock in August 2018. Employee Stock Purchase Plan Our board of directors has adopted and our stockholders have approved our 2018 Employee Stock Purchase Plan ("2018 ESPP"). Our 2018 ESPP became effective on February 8, 2018, the date our registration statement in connection with our IPO was declared effective and enables eligible employees to purchase shares of our common stock at a discount. Purchases will be accomplished through participation in discrete offering periods. On each purchase date, eligible employees will purchase our common stock at a price per share equal to 85% of the lesser of the fair market value of our common stock on the first trading day of the offering period or the date of purchase. Upon the completion of our first offering period on November 15, 2018, 177,238 shares of common stock were purchased by employees under the 2018 ESPP. Initially, the aggregate number of shares of our common stock that may be issued pursuant to our 2018 ESPP is 375,000 shares. Additionally, the number of shares of our common stock reserved for issuance under our 2018 ESPP will automatically increase on January 1 of each year, beginning on January 1, 2019 and continuing through and including January 1, 2026, by the lesser of (i) 1% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year, (ii) 500,000 shares of our common stock or (iii) such lesser number of shares of common stock as determined by our board of directors. Accordingly, the number of shares of our common stock reserved for issuance under our 2018 ESPP increased by 224,662 shares on January 1, 2019. Shares subject to purchase rights granted under our 2018 ESPP that terminate without having been exercised in full will not reduce the number of shares available for issuance under our 2018 ESPP.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Domestic and foreign components of loss before income taxes are as follows (in thousands): Year Ended December 31, 2016 2017 2018 Domestic $ (73,167 ) $ (16,711 ) $ (48,897 ) Foreign (2,529 ) (2,930 ) (4,145 ) Loss before income taxes $ (75,696 ) $ (19,641 ) $ (53,042 ) The significant components of income tax (expense) benefit are as follows (in thousands): Year Ended December 31, 2016 2017 2018 Current: Federal $ — $ — $ — State — — — Foreign — — — Total current — — — Deferred: Federal 22,449 (28,331 ) 6,896 State 1,796 2,345 1,264 Foreign 864 85 916 Change in uncertain tax positions (117 ) (120 ) (105 ) Change in valuation allowance (24,992 ) 26,021 (8,971 ) Total deferred — — — Income tax benefit $ — $ — $ — The following table summarizes the significant differences between the U.S. federal statutory tax rate and our effective tax rate: Year Ended December 31, 2016 2017 2018 Tax benefit at federal statutory rate 34.00 % 34.00 % 21.00 % State income taxes, net of federal benefit 1.36 % 1.82 % 1.91 % Change in federal and state statutory rate — % (156.32 )% 0.03 % Foreign rate differential (0.80 )% (1.04 )% (0.06 )% Other adjustments (1.54 )% (10.93 )% (5.97 )% Valuation allowance (33.02 )% 132.47 % (16.91 )% Income tax benefit — % — % — % The significant components of deferred income taxes are as follows (in thousands): December 31, 2017 2018 Net operating loss carry-forwards $ 53,182 $ 60,718 Allowance for doubtful accounts 18 26 Depreciation and amortization (485 ) (856 ) Stock-based compensation 1,330 1,968 Deferred costs 1,042 1,334 IRC Section 163(j) interest expense limitation — 737 Other tax credit carry-forward 2,720 3,071 Other temporary differences 842 465 Valuation allowance (58,649 ) (67,463 ) Net long-term deferred tax liability $ — $ — On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (“Tax Act”) was signed into law making significant changes to the IRC. Changes include, but are not limited to, a corporate tax rate decrease to 21% effective for tax years beginning after December 31, 2017 . This change in tax rate resulted in a reduction in our net U.S. deferred tax assets, which was fully offset by a reduction in our valuation allowance. The other provisions of the Tax Act, including the one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings, did not have a material impact on our financial statements as of December 31, 2018 . We have generated historical net losses and recorded a full valuation allowance against our net deferred tax assets. We expect to maintain a full valuation allowance in the near term. Realization of any of our net deferred tax assets depends upon future earnings, the timing and amount of which are uncertain. The following table presents changes in our valuation allowance (in thousands): Year Ended December 31, 2016 2017 2018 Beginning balance $ (59,789 ) $ (84,483 ) $ (58,649 ) Allowance for domestic and foreign net operating loss carry-forwards (24,791 ) (6,509 ) (9,863 ) Rate change on domestic net operating loss carry-forwards (15 ) 30,705 (17 ) Change in foreign currency 298 (187 ) 157 Other changes (186 ) 1,825 909 Ending balance $ (84,483 ) $ (58,649 ) $ (67,463 ) As of December 31, 2017 and 2018 we have $220.5 million and $249.8 million , respectively, of gross U.S. federal net operating loss carry forwards that will begin to expire in the 2028 tax year. Additionally, we have $76.3 million and $90.5 million of gross state net operating loss carry-forwards as of December 31, 2017 and 2018 , respectively that will also begin to expire in the 2028 tax year. Ownership changes, as defined by IRC Section 382, may limit the amount of net operating losses that a company may utilize to offset future taxable income and taxes payable. Pursuant to IRC Section 382, an ownership change occurs when the stock ownership of 5% stockholders increases by more than 50% over a testing period of three years . We completed an evaluation of the potential effect of IRC Section 382 on our net operating losses after the completion of our convertible promissory note financing in 2016 and concluded that we had not experienced an ownership change in the past three years as of that date. We also completed an evaluation through February 8, 2018 , the date of our initial listing on the Nasdaq Global Market, and there are no indications that an ownership change has occurred through this date. It is possible that we have subsequently undergone an ownership changes as defined by IRC Section 382 or that we may undergo such a change in the future. Any such ownership change may limit our ability to utilize net operating losses. Our results during 2016 , 2017 and 2018 reflect state tax credits related to hiring and research activities that are utilized through the reduction of state payroll tax withholdings totaling $0.6 million , $0.8 million and $0.7 million , respectively. As of December 31, 2017 and 2018 , Cardlytics UK had gross net operating losses of $11.4 million and $13.9 million , respectively. Foreign net operating loss carry-forwards expire according to the rules of each country. In the U.K., there is an indefinite carry-forward period. As of December 31, 2018 , Cardlytics UK held cash and cash equivalents of $3.8 million . While our investment in Cardlytics UK is not considered to be permanently invested, we do not plan to repatriate these funds. Further, although the tax basis of our investment in Cardlytics UK exceeds its book basis, we have not recorded a deferred tax asset since we do not believe that a reversal of this temporary difference will occur in the foreseeable future. The following table summarizes the activity related to our gross unrecognized tax benefits that would affect our effective tax rate, if recognized (in thousands): Year Ended December 31, 2016 2017 2018 Beginning balance $ 441 $ 558 $ 678 Increase related to current year tax position 117 120 105 Ending balance $ 558 $ 678 $ 783 All such positions, if recognized, would impact our effective tax rate. We do not currently anticipate any of our positions to change significantly in the next 12 months. Our tax filings from inception remain subject to income tax examinations.

REDEEMABLE CONVERTIBLE PREFERRE

REDEEMABLE CONVERTIBLE PREFERRED STOCK	12 Months Ended
	Dec. 31, 2018
Temporary Equity Disclosure [Abstract]
REDEEMABLE CONVERTIBLE PREFERRED STOCK	REDEEMABLE CONVERTIBLE PREFERRED STOCK Upon the consummation of our IPO, all of the outstanding shares of redeemable convertible preferred stock were automatically converted into shares of common stock. Refer to Note 1—Nature of Operations for additional information regarding our IPO. A summary of the change in carrying amount of the outstanding redeemable convertible preferred stock is as follows (in thousands): Series G’ Stock Series G Stock Shares Amount Shares Amount Balance — December 31, 2016 — $ — — $ — Issuance of Series G and Series G’ Stock 1,296 44,672 346 4,488 Beneficial conversion feature of Series G stock — — — (4,488 ) Deemed dividend related to beneficial conversion feature 4,488 Accretion of redeemable convertible preferred stock — — — 622 Balance — December 31, 2017 1,296 44,672 346 5,110 Accretion of redeemable convertible preferred stock — — — 108 Conversion of preferred stock to common stock (1,296 ) (44,672 ) (346 ) (5,218 ) Balance — December 31, 2018 — $ — — $ — Series F/F-R Stock Series E/E-R Stock Series D/D-R Stock Shares Amount Shares Amount Shares Amount Balance — December 31, 2015 1,199 $ 57,204 1,193 $ 44,922 1,396 $ 32,509 Accretion of redeemable convertible preferred stock — 754 — 19 — 133 Conversion of preferred stock to common stock — — (398 ) (14,978 ) — — Balance — December 31, 2016 1,199 $ 57,958 795 $ 29,963 1,396 $ 32,642 Accretion of redeemable convertible preferred stock — 491 — 9 — 86 Balance — December 31, 2017 1,199 $ 58,449 795 $ 29,972 1,396 $ 32,728 Accretion of redeemable convertible preferred stock — 38 — 1 — 7 Conversion of preferred stock to common stock (1,199 ) (58,487 ) (795 ) (29,973 ) (1,396 ) (32,735 ) Balance — December 31, 2018 — $ — — $ — — $ — Series C/C-R Stock Series B/B-R Stock Series A/A-R Stock Shares Amount Shares Amount Shares Amount Balance — December 31, 2015 1,508 $ 18,254 2,249 $ 5,287 1,869 $ 1,885 Accretion of redeemable convertible preferred stock — 69 — 4 — 3 Conversion of preferred stock to common stock — — (2 ) (5 ) (12 ) (38 ) Balance — December 31, 2016 1,508 $ 18,323 2,247 $ 5,286 1,857 $ 1,850 Accretion of redeemable convertible preferred stock — 43 — 2 — 2 Balance — December 31, 2017 1,508 $ 18,366 2,247 $ 5,288 1,857 $ 1,852 Accretion of redeemable convertible preferred stock — 3 — — — — Conversion of preferred stock to common stock (1,508 ) (18,369 ) (2,247 ) (5,288 ) (1,857 ) (1,852 ) Balance — December 31, 2018 — $ — — $ — — $ — During the second quarter of 2016, we issued convertible promissory notes to our founders and the existing holders of our redeemable convertible preferred stock. Shares of redeemable convertible preferred stock held by investors that participated in the financing were exchanged for shares of replacement preferred stock. Replacement shares were issued for 1,856,998 shares of Series A Stock, 2,246,744 shares of Series B Stock, 1,507,906 shares of Series C Stock, 1,395,936 shares of Series D Stock, 795,027 shares of Series E Stock and 1,198,637 shares of Series F Stock. These replacement shares have rights and preferences equal to their corresponding original series and are designated as Series A-R Stock, Series B-R Stock, Series C-R Stock, Series D-R Stock, Series E-R Stock and Series F-R Stock. Shares of redeemable convertible preferred stock held by investors that did not participate in the financing were converted to common stock and consisted of 12,375 shares of Series A Stock, 2,121 shares of Series B Stock and 397,515 shares of Series E Stock. In February 2017, we amended and restated our certificate of incorporation reducing the authorized number of shares of our redeemable convertible preferred stock to 82,683,212 and canceled Series A Stock, Series B Stock, Series C Stock, Series D Stock, Series E Stock and Series F Stock. Pursuant to our convertible promissory note financing, these series of preferred stock were either exchanged for shares of replacement preferred stock with rights and preferences equal to their corresponding original series or converted to common stock. Series G Stock Financing In May 2017, we amended and restated our certificate of incorporation and increased the authorized number of shares of our common stock to 83,000,000 and increased the authorized number of shares of our redeemable convertible preferred stock to 96,131,002 . In May 2017, we issued and sold, for aggregate consideration of $11.9 million , an aggregate of 346,334 shares of Series G redeemable convertible preferred stock, par value $0.0001 per share with a stated price of $34.4758 per share (“Series G Stock”), and warrants to purchase shares of our common stock. Issuance costs incurred in connection with the sale of Series G Stock totaled $0.1 million . Conversion of Convertible Promissory Notes into Series G’ Stock In connection with the Series G Stock financing in May 2017, certain convertible promissory notes converted into 1,295,746 shares of Series G’ redeemable convertible preferred stock, par value $0.0001 per share (“Series G’ Stock”), at a price per share of $27.58 . Common Stock Warrants Issued in Connection with the Series G Stock Financing In connection with the Series G Stock financing, we issued warrants to purchase an aggregate of number of shares of common stock equal to the product obtained by multiplying 346,334 by a fraction, the numerator of which is the difference between $68.9516 and the volume weighted average closing price of our common stock over the 30 trading days (or such lesser number of days as our common stock has been traded on the Nasdaq Global Market) prior to the date on which such warrants vest and become exercisable and the denominator of which is such volume weighted average closing price, which warrants vested and became exercisable on August 8, 2018, which was 180 days following the date of our IPO, at an exercise price of $0.0004 per share. In August 2018, we issued warrants to purchase 792,434 shares of common stock at an exercise price of $0.0004 per share to the cash investors of our Series G financing, pursuant to our Series G stock purchase agreement. The warrants had a valuation of $15.3 million upon issuance and were immediately exercised. Refer to Note 10—Fair Value Measurement for additional information regarding the valuation of the warrants issued in connection with the Series G Stock financing. Beneficial conversion feature The aggregate proceeds of $11.9 million from the Series G Stock financing were first allocated to the warrants to purchase shares of our common stock, which qualify as liabilities under ASC 480 and are recorded at fair value, with the residual value of $4.5 million allocated to our Series G Stock. As a result of this allocation, Series G Stock was determined to contain a beneficial conversion feature with an intrinsic value of $6.1 million . The amount assigned to the beneficial conversion feature was limited to the $4.5 million residual value allocated to Series G Stock and is classified as a component of additional paid-in capital. During the second quarter of 2017, we recorded a deemed dividend of $4.5 million related to the beneficial conversion feature, which is reflected below net loss to arrive at net loss available to common stockholders. Series G’ In connection with the Series G Stock financing, the Existing Stockholder Notes and the Outstanding Obligation Note converted into 1,295,746 shares of Series G’ redeemable convertible preferred stock, par value $0.0001 per share (“Series G’ Stock”), at a price per share of $2.758 . The Series G’ Stock carries a stated dividend of $2.758 per annum, payable quarterly when, as, and if declared by our board of directors. These dividends are noncumulative in nature. The Series G’ Stock is entitled to certain anti-dilution protections. Series F / Series F-R In connection with the Series F Stock financing, investors also purchased 199,771 shares of common stock from certain members of management at the purchase price of $50.0568 per share for aggregate consideration of $10.0 million . The difference between the $50.0568 purchase price and the $24.40 transaction date fair value per share of our common stock amounted to $5.1 million and is recorded in general and administrative expense. Placement fees of $3.6 million and $0.5 million were allocated to the Series F Stock financing and secondary sale of common stock, respectively. Fees allocated to the Series F Stock financing were recorded as a net reduction in sale proceeds and the fees allocated to the secondary sale of common stock are included in general and administrative expense. Redemption At any time on or after May 4, 2022, upon written request of the holders of not less than 66 2 / 3 % of the shares of redeemable convertible preferred stock then-outstanding, voting together as a single class on an as-converted to common stock basis, we are required to redeem all outstanding shares of redeemable convertible preferred stock in eight quarterly installments. The Series A-R Stock, Series B-R Stock, Series C-R Stock, Series D-R Stock, Series E-R Stock, Series F-R Stock, Series G Stock and Series G’ Stock are redeemable at prices equal to $1.00 , $2.3567 , $12.2686 , $23.64 , $37.7344 , $58.40 , $34.4758 and $34.4758 per share, plus any declared or accumulated but unpaid dividends, respectively. To the extent that we have insufficient funds to redeem all outstanding shares of redeemable convertible preferred stock, we are required to first redeem shares of Series G Stock and Series G’ Stock, then shares of Series F/F-R Stock, then shares of Series E/E-R Stock, then shares of Series D/D-R Stock, then shares of Series C/C-R Stock and then shares of Series B/B-R Stock and Series A/A-R Stock pari passu , in each case on a pro rata basis among the holders thereof. The redeemable convertible preferred stock carrying amount is increased by periodic accretions, using the interest method, so that the carrying amount will equal the redemption amount at May 4, 2022. Accretion is recorded through a charge against additional paid-in capital. Liquidation Upon us (i) selling or otherwise disposing of all or substantially all of our property or business or merging with or into or consolidation with any other corporation, limited liability company or other entity, (ii) a majority of the voting power of our outstanding capital stock being transferred or disposed of as a result of a transaction or series of related transactions that are not issuances of capital stock by us primarily for the purposes of raising equity capital or (iii) any dissolution or winding-up of our business, the holders of Series G’ Stock, Series G Stock, Series F-R Stock, Series E-R Stock, Series D-R Stock, Series C-R Stock, Series B-R Stock and Series A-R Stock shall be entitled to receive payments in amounts per share equaling $34.4758 , $68.9516 , $58.40 , $37.7344 , $23.64 , $21.4701 , $2.3567 and $1.00 , plus any declared but unpaid dividends, respectively. Holders of Series G Stock and Series G’ Stock are pari passu and are to be paid prior, and in preference to, any distribution of assets to the holders of all other classes of capital stock. Holders of Series F-R Stock are to be paid prior, and in preference to, any distribution of assets to the holders of Series E-R Stock, Series D-R Stock, Series C-R Stock, Series B-R Stock and Series A-R Stock. Holders of Series E-R Stock are to be paid prior, and in preference to, any distribution of assets to the holders of Series D-R Stock, Series C-R Stock, Series B-R Stock and Series A-R Stock. Holders of Series D-R Stock are to be paid prior, and in preference to, any distribution of assets to the holders of Series C-R Stock, Series B-R Stock and Series A-R Stock. Holders of Series C-R Stock are to be paid prior, and in preference to, any distribution of assets to the holders of Series B-R Stock and Series A-R Stock. Holders of Series A-R Stock and Series B-R Stock are pari passu and are to be paid prior, and in preference to, any distribution of assets to the holders of common stock. Upon completion of the distributions detailed above, any remaining assets are to be distributed to the holders of common stock, Series A-R Stock, Series B-R Stock, Series C-R Stock, Series D-R Stock, Series E-R Stock, Series F-R Stock, Series G Stock and Series G’ Stock; such participation in the distribution of remaining assets shall cease, however, when the amount that the holders of Series A-R Stock, Series B-R Stock, Series C-R Stock, Series D-R Stock, Series E-R Stock, Series F-R Stock, Series G Stock and Series G’ Stock are entitled to receive upon liquidation equals $2.00 per share, $4.7134 per share, $36.8058 per share, $70.92 per share, $113.2032 per share, $175.20 per share, $103.4274 per share and $103.4274 per share, respectively, plus any declared but unpaid dividends thereon. If, however, as a result of a conversion from redeemable convertible preferred stock to common stock, a holder would receive, in the aggregate, an amount greater than the amount that would be distributed to such holder if such holder did not convert such series of redeemable convertible preferred stock into shares of common stock, such holder shall be deemed to have converted such holder’s shares of redeemable convertible preferred stock into shares of common stock for the purposes of determining the amount that such holder is entitled to receive upon liquidation and shall not be entitled to any distribution that would have otherwise been made to the holders of redeemable convertible preferred stock detailed above. Dividends No dividends have been declared or paid as of December 31, 2018 . Conversion The holders of our redeemable convertible preferred stock also had the right, at any time, to convert any or all of their shares into such number of shares of common stock as is determined by dividing $1.00 in the case of Series A-R Stock, $2.3567 in the case of the Series B-R Stock, $12.2686 in the case of Series C-R Stock, $23.64 in the case of Series D-R Stock, $37.7344 in the case of Series E-R Stock, $50.0568 in the case of Series F-R Stock, and $34.4758 in the case of Series G Stock and Series G’ Stock by the applicable conversion price. The initial conversion price is $1.00 in the case of Series A-R Stock, $2.3567 in the case of the Series B-R Stock, $12.2686 in the case of Series C-R Stock, $23.64 in the case of Series D-R Stock, $37.7344 in the case of Series E-R Stock, $50.0568 in the case of Series F-R and $34.4758 in the case of Series G Stock and Series G’ Stock. If, at any time following the initial issuance of shares of Series G Stock, we issue any additional shares of capital stock without consideration or for a consideration per share less than the then-effective conversion price for our redeemable convertible preferred stock, the conversion price for all series of outstanding redeemable convertible preferred stock are subject to adjustment. There have been no changes to the conversion price for any series of redeemable convertible preferred stock as of December 31, 2018 .

COMMON STOCK WARRANTS

COMMON STOCK WARRANTS	12 Months Ended
	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
COMMON STOCK WARRANTS	COMMON STOCK WARRANTS We have granted warrants to purchase shares of our common stock to certain FI partners that include both time-based and performance-based vesting conditions. These warrants are accounted for under ASC Topic 505-50, Equity-Based Payments to Non-Employees . Since the performance conditions contained in these warrants are directly related to revenue-producing activities, we incur non-cash expense in FI Share and other third-party costs on our consolidated statements of operations based on the vesting-date fair value of our common stock underlying these warrants. A summary of common stock warrant activity, exclusive of the common stock warrants issued in connection with our Series G financing is as follows (in thousands, except per share amounts): Shares Weighted-average exercise price per share Warrants Outstanding - December 31, 2015 448 $ 5.28 Granted 97 20.00 Redeemable convertible preferred stock warrants converted to common stock warrants 38 1.92 Warrants Outstanding - December 31, 2016 583 7.52 Granted 17 27.68 Warrants Outstanding - December 31, 2017 600 8.11 Granted (1) 644 23.64 Exercised (349 ) 4.69 Redeemable convertible preferred stock warrants converted to common stock warrants 110 12.16 Forfeited/canceled (138 ) 5.85 Warrants Outstanding - December 31, 2018 867 $ 21.89 (1) Performance-based warrants to purchase 644,365 shares of our Series E Stock, which were converted to common stock warrants, vested upon the completion of our IPO in February 2018. These warrants are not included within this table in periods prior to their vesting. Pursuant to the Term Loan, in July 2016, we issued 10-year fully vested warrants to purchase 97,125 shares of common stock at an exercise price of $20.00 per share. In June 2017, we issued additional warrants to purchase 17,500 shares of common stock at a price of $27.68 per share. During 2016 , warrants to purchase shares of redeemable convertible preferred stock held by parties that did not participate in the Existing Stockholder Note financing were converted to common stock warrants. As a result, fully vested warrants to purchase 12,500 shares of our Series A Stock at an exercise price of $1.00 per share, fully vested warrants to purchase 25,000 shares of our Series B Stock at an exercise price of $2.36 per share and unvested performance-based warrants to purchase 644,365 shares of our Series E Stock at an exercise price of $23.64 per share were converted to common stock warrants. The performance-based warrants to purchase 644,365 shares of our Series E Stock, which were converted to common stock warrants, vested upon the consummation of our IPO in February 2018 as discussed in Note 11—Related Parties. The conversion date fair value of the Series A Stock warrants and Series B Stock warrants, which were converted to common stock warrants, was reclassified from redeemable convertible preferred stock warrant liability to additional paid-in capital. See Note 10—Fair Value Measurements for more information.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASURMENTS	FAIR VALUE MEASUREMENTS Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The following table summarizes our liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Liabilities: Preferred stock warrants (1) $ — $ — $ 2,285 $ 2,285 Common stock warrants (1) — — 7,945 7,945 Total liabilities $ — $ — $ 10,230 $ 10,230 (1) Warrant liabilities were zero as of December 31, 2018 . Instruments Recorded at Fair Value Using Level 3 Inputs Our redeemable convertible preferred stock warrants, common stock warrants issued in connection with the Series G Stock financing and our convertible promissory notes are measured and recorded at fair value on a recurring basis using Level 3 inputs. The table below provides a roll forward of the changes in fair value of Level 3 financial instruments (in thousands): Preferred Common Convertible Balance at December 31, 2015 $ 2,942 — $ — Fair value of convertible promissory notes at issuance — — 66,391 Accrued interest on convertible promissory notes — — 2,876 Conversion of preferred stock warrants to common stock warrants (777 ) — — Changes in fair value 32 — 3,065 Balance at December 31, 2016 $ 2,197 $ — $ 72,332 Preferred Common Convertible Balance at December 31, 2016 $ 2,197 $ — $ 72,332 Conversion of convertible promissory notes to Series G’ preferred stock — — (44,672 ) Conversion of convertible promissory notes to common stock — — (24,392 ) Accrued interest on convertible promissory notes — — 1,701 Issuance of common stock warrants — 7,452 — Changes in fair value 88 493 (4,969 ) Balance at December 31, 2017 $ 2,285 $ 7,945 $ — Preferred Stock Warrants Common Stock Warrants Convertible Promissory Notes Balance at December 31, 2017 $ 2,285 $ 7,945 $ — Conversion of preferred stock warrants to common stock warrants (1,736 ) — — Changes in fair value (549 ) 7,309 — Exercise of common stock warrants — (15,254 ) — Balance at December 31, 2018 $ — $ — $ — In valuing our instruments recorded at fair value using Level 3 inputs, our board of directors determined the equity value of our business generally using a combination of the income approach and the market approach valuation methods. The income approach estimates value based on the expectation of future cash flows that a company will generate, such as cash earnings, cost savings, tax deductions and the proceeds from disposition. These future cash flows are discounted to their present values using a discount rate derived based on an analysis of the cost of capital of comparable publicly traded companies in similar lines of business, as of each valuation date, and is adjusted to reflect the risks inherent in our cash flows. The market approach estimates the fair value of a company by applying market multiples of comparable publicly traded companies in a similar line of business. The market multiples are based on relevant metrics implied by the price that investors have paid for the equity of publicly traded companies. Given our significant focus on investing in and growing our business, we primarily utilized the forward-looking revenue multiple when performing valuation assessments under the market approach and considered both trading and transaction multiples. When considering which companies to include as our comparable industry peer companies, we focused on U.S.-based publicly traded companies that were broadly comparable to us based on consideration of industry, market and line of business. From the comparable companies, a representative market value multiple was determined and applied to our operating results to estimate the value of our company. The market value multiple was determined based on consideration of multiples of revenue to each of the comparable companies’ historical and forecasted revenue. In addition, the market approach considers IPO and merger and acquisition transactions involving companies similar to the company’s business being valued. Multiples of revenue are calculated for these transactions and then applied to the business being valued, after reduction by an appropriate discount. Once an equity value was determined, we utilized the option pricing method ("OPM"), or probability-weighted expected return method (“PWERM”) to allocate the overall value of equity to the various share classes. The OPM was used in valuations as of and for dates prior to December 31, 2016 and the PWERM was used in all subsequent valuations. The OPM treats common stock and convertible preferred stock as call options on a company’s enterprise value with exercise prices based on the liquidation preferences of the convertible preferred stock. Under this method, the common stock only has value if the funds available for distribution to stockholders exceed the value of the liquidation preference at the time of an assumed liquidity event. The value assigned to the common stock is the remaining value after the convertible preferred stock is liquidated. The OPM prices the call option using the Black-Scholes model. The PWERM relies on a forward-looking analysis to predict the possible future value of a company. Under this method, discrete future outcomes, including an IPO and non-IPO scenarios, are weighted based on the estimated the probability of each scenario. The PWERM is used when discrete future outcomes can be predicted with reasonable certainty based on a probability distribution. We relied on the PWERM to allocate the value of equity under a liquidity scenario. The projected equity value relied upon in the PWERM scenario was based on (i) guideline IPO transactions involving companies that were considered broadly comparable to us and (ii) our expectation of the pre-money valuation that we needed to achieve to consider an IPO as a viable exit strategy. The following table summarizes key assumptions used in the PWERM for estimating the fair value of our redeemable convertible preferred stock warrant liability: December 31, 2016 2017 Cost of debt applicable to convertible promissory notes 12% to 17% —% Cost of equity applicable to convertible promissory notes 24% to 26% —% Weighted-average cost of capital applicable to preferred stock warrants 23% 21% Discount for lack of marketability 8% to 12% 7% to 13% Volatility 54% 55% Risk-free interest rate 0.7% to 1.2% 1.2% to 1.4% Preferred Stock Warrants Upon the consummation of our IPO, all of the outstanding warrants to purchase shares of redeemable convertible preferred stock were automatically converted into warrants to purchase shares of common stock. Refer to Note 8—Redeemable Convertible Preferred Stock for additional information regarding our IPO. A summary of our preferred stock warrants is as follows (in thousands, except per share amounts): December 31, Preferred Series Grant date Expiration date Exercise price 2016 2017 2018 Series B-R 2/26/2010 2/25/2020 $ 2.36 59 59 — Series D-R 9/21/2012 9/20/2022 $ 23.64 38 38 — Series D-R 9/21/2012 9/20/2022 $ 23.64 13 13 — Total preferred stock warrants 110 110 — On May 26, 2016, warrants to purchase shares of redeemable convertible preferred stock held by parties that did not participate in the Existing Stockholder Note financing were converted to common stock warrants. As a result, warrants to purchase 12,500 shares of our Series A Stock, 25,000 shares of our Series B Stock and 644,365 shares of our Series E Stock were converted to common stock warrants. The performance-based warrants to purchase 644,365 shares of our Series E Stock, which were converted to common stock warrants, vested upon the completion of our IPO in February 2018 as discussed in Note 11—Related Parties. The conversion date fair value of the Series A Stock warrants and Series B Stock warrants, which were converted to common stock warrants, was reclassified from redeemable convertible preferred stock warrant liability to additional paid-in capital. We determined that a retrospective valuation of the fair value of our preferred stock warrants on the conversion date was appropriate for financial reporting purposes. In connection with the preparation of our retrospective valuation, we noted that the fair value of our Series B Stock warrants decreased from $20.48 per share on April 30, 2016 to $18.16 per share on September 30, 2016. The decrease in the fair value of the Series B Stock warrants primarily resulted from the dilutive effect of issuing our convertible promissory notes as the Company’s enterprise values on April 30, 2016 and September 30, 2016 were similar and there were no events, or series of events, other than the issuance of the convertible promissory notes, which would have clearly resulted in a decrease in the fair value of the Series B Stock warrants. We derived the fair value of the Series B Stock warrants on the conversion date using an interpolation methodology that considered both the timing and amount of dilution from issuing convertible promissory notes and determined the conversion date fair value to be $20.36 per share. The fair value of our Series A Stock warrants was $21.56 per share on April 30, 2016. Historically, the fair value of our Series A Stock warrants have changed in a similar pattern to our Series B Stock warrants due to similarities between the underlying Series A Stock and Series B Stock. We determined the conversion date fair value to be $21.44 per share based on similar percentage decline in the fair value of our Series B Stock. The fair value of the warrants to purchase Series B-R Stock and Series D-R Stock decreased from $26.80 per share and $13.63 per share on December 31, 2017 to $20.18 per share and $10.57 per share on February 8, 2018, respectively, the date at which they converted to warrants to purchase shares of our common stock and were reclassified to additional paid-in capital on our consolidated balance sheet. The decrease in the fair value of the warrants to purchase Series B-R Stock and Series D-R Stock primarily resulted from the timing of future potential liquidity events, changes to our forecasted financial results and changes in the valuation of comparable companies. Common Stock Warrants In July 2016, we issued warrants to purchase 97,125 shares of common stock at an exercise price of $20.00 per share to a lender. In June 2017, we issued the lender additional warrants to purchase 17,500 shares of common stock at a price of $27.68 per share. The fair value of the warrants issued in July 2016 and June 2017 were calculated to be $1.0 million and $0.3 million , respectively. We determined the grant date fair value of these common warrants using the Black-Scholes option pricing model, which is affected by the estimated fair value of our common stock as well as the following significant inputs: Common stock Common stock Weighted-average grant date fair value $10.44 $19.04 Significant inputs: Value of common stock $17.92 $30.08 Expected term 10 years 10 years Volatility 51% 50% Risk-free interest rate 1.2% 2.2% Dividend yield —% —% Common Stock Warrants Issued in Connection with the Series G Stock Financing In connection with the Series G Stock financing, we issued warrants to purchase an aggregate number of shares of common stock equal to the product obtained by multiplying 346,334 by a fraction, the numerator of which is the difference between $68.9516 and the volume weighted average closing price of our common stock over the 30 trading days (or such lesser number of days as our common stock has been traded on the Nasdaq Global Market) prior to the date on which such warrants vest and become exercisable and the denominator of which is such volume weighted average closing price, which warrants vested and became exercisable on August 8, 2018, which was 180 days following the date of our IPO, at an exercise price of $0.0004 per share. To determine the fair value of our common stock warrant liability issued in connection with our Series G Stock financing, we utilized a Monte Carlo simulation, which allows for the modeling of complex securities and evaluates many possible outcomes to forecast the stock price of the company post-IPO. As part of the valuation, we considered various scenarios related to the pricing, timing and probability of an IPO. We applied an annual equity volatility of 59% and a discount for lack of marketability of 11% to arrive at a valuation of $7.5 million on the issuance date. Subsequent to our IPO, the fair value of the common stock warrant liability was estimated based on the fair market value of our common stock at each reporting period, discounted from the date of settlement. In August 2018, we issued warrants to purchase 792,434 shares of common stock at an exercise price of $0.0004 per share to the cash investors of our Series G financing, pursuant to our Series G stock purchase agreement. The warrants had a valuation of $15.3 million upon issuance and were subsequently exercised, resulting in the issuance of 792,434 shares of our common stock. As a result of change in fair value of the common stock warrant liability, we recognized non-cash losses of $0.5 million and $7.3 million in 2017 and 2018 , respectively. Convertible Promissory Notes Refer to Note 8—Redeemable Convertible Preferred Stock for additional information of the Series G Stock financing and the transactions that resulted in the conversion of the convertible promissory notes into shares of our Series G’ Stock. The redemption features included in the terms of the convertible promissory notes were determined to be derivative liabilities due to a significant discount within the redemption features for the note holders. Embedded derivatives that are not clearly and closely related to the host contract are required to be bifurcated and recorded at fair value unless the fair value option is elected on the host contract. Under the fair value option, bifurcation of the embedded derivative is not necessary as all related gains (losses) on the host contract and derivative will be reflected in the consolidated statements of operations. We elected the fair value option for the Existing Stockholder Notes and Aimia Notes, therefore direct costs and fees associated with the issuance were recognized in earnings as incurred and were not deferred. To determine the fair value of our convertible promissory notes, we utilized key assumptions from the PWERM, as shown above. Under this method, we considered the redemption features of the convertible promissory notes, as described in Note 5—Debt for additional information, to determine the fair value under discrete future outcomes, including IPO and non-IPO scenarios. Under certain non-IPO scenarios, holders of the convertible promissory notes were due to receive two times preference on the outstanding principal amount. We weighted the fair values based on the estimated probability of each scenario to determine the overall fair value of the convertible promissory notes as of the balance sheet date. Performance-based Warrants Issued to FIS In May 2013, we granted 10 -year performance-based warrants to purchase up to 644,365 shares of Series E Stock at an exercise price of $23.64 per share. Since FIS did not participate in the convertible promissory note financing, their warrants to purchase preferred stock were converted to warrants to purchase common stock. The warrants vested upon the completion of our IPO in February 2018 resulting in a non-cash expense of $2.5 million . We determined the fair value of these common warrants on the date of IPO using the Black-Scholes option pricing model, which is affected by the fair value of our common stock as well as the following significant inputs: February 8, 2018 Weighted-average grant date fair value $3.91 Significant inputs: Value of common stock $13.00 Expected term 5.3 years Volatility 50% Risk-free interest rate 2.0% Dividend yield —%

RELATED PARTIES

RELATED PARTIES	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
RELATED PARTIES	RELATED PARTIES Convertible Promissory Notes As discussed in Note 5—Debt, in 2016 , we issued Existing Stockholder Notes to our founders and certain of our existing stockholders in an aggregate principal amount of $27.0 million . The following table summarizes purchases of our convertible promissory notes by our directors, executive officers and holders of more than 5% of any class of our capital stock as of the date of such transaction (in thousands): Related Party Principal amount of convertible notes Aeroplan Holdings Europe Sàrl(1) $ 3,987 Entities affiliated with Polaris Venture Partners(2) 5,321 Canaan VIII L.P.(3) 6,514 Entities affiliated with Discovery Capital(4) 2,663 Scott D. Grimes 650 Lynne M. Laube 350 (1) Aeroplan Holdings Europe Sàrl is an affiliate of Aimia Inc. David L. Adams, a member of our board of directors, was the Executive Vice President and Chief Financial Officer of Aimia Inc. at the time of the issuance. (2) Consists of convertible promissory notes in an aggregate principal amount of $5,134,443.03 purchased by Polaris Venture Partners V, L.P. ("PVP V") convertible promissory notes in an aggregate principal amount of $100,069.82 purchased by Polaris Venture Partners Entrepreneurs’ Fund V, L.L. ("PVP EF V") convertible promissory notes in an aggregate principal amount of $35,170.61 purchased by Polaris Venture Partners Founders’ Fund V, L.P. ("PVP FF V") and convertible promissory notes in an aggregate principal amount of $51,344.45 purchased by Polaris Venture Partners Special Founders’ Fund V, L.P. ("PVP SFF V") Polaris Venture Management Co. V, L.L.C. (“PVM V”) is the general partner of each PVP V, PVP EF V, PVP FF V, and PVP SFF V (collectively, the “Polaris Funds”). PVM V may be deemed to have sole power to vote and dispose of the shares held by each of the Polaris Funds. Each of Jonathan Flint and Terrance McGuire (collectively, the “Managing Members”) are the managing members of PVM V and may be deemed to share voting and dispositive power with respect to the shares held by the Polaris Funds. Bryce Youngren, a member of our board of directors, has a membership interest in PVM V, and may be deemed to share voting and dispositive powers with respect to the shares held by the Polaris Funds by virtue of his relationship to PVM V. Each of PVM V, the Managing Members and Mr. Youngren disclaim beneficial ownership of all of the shares owned by the Polaris Funds, and this report shall not be deemed an admission that any of PVM V, the Managing Members or Mr. Youngren is the beneficial owner of the shares owned by the Polaris Funds for purposes of Section 16 or for any other purpose, except to the extent of their respective and proportionate pecuniary interests therein. (3) John V. Balen, a member of our board of directors, is a managing member of Canaan Partners VIII LLC, the general partner of Canaan VIII L.P. Mr. Balen does not have voting or investment power over any shares held directly by Canaan VIII L.P. (4) Consists of convertible promissory notes in an aggregate principal amount of $2,385,974.51 purchased by Discovery Global Opportunity Master Fund, Ltd. ("Discovery Global Opportunity") and convertible promissory notes in an aggregate principal amount of $277,291.57 purchased by Discovery Global Focus Master Fund, Ltd. ("Discovery Global Focus") Discovery Capital Management, LLC is the manager of each of Discovery Global Opportunity and Discovery Global Focus, and may be deemed to have the sole voting and dispositive power over the shares held by Discovery Global Opportunity and Discovery Global Focus. Series G / Series G’ In May 2017, we issued and sold, for aggregate consideration of $11.9 million , an aggregate of 346,334 shares of our Series G Stock and warrants to purchase shares of our common stock. In connection with the issuance of our Series G Stock, the principal and accrued interest under the convertible promissory notes converted into an aggregate of 1,295,746 shares of our Series G’ redeemable convertible preferred stock and 801,329 shares of our common stock. The following table summarizes the participation in the foregoing transactions by our directors, executive officers and holders of more than 5% of any class of our capital stock as of the date of such transactions (in thousands): Related Party Shares of Series G Preferred Stock Shares of Series G’ Preferred Stock Shares of Common Stock Warrants to Purchase Common Stock Entities affiliated with Aimia, Inc. (1) — 382 801 — Entities affiliated with Polaris Venture Partners (2) 29 212 — 66 Canaan VIII L.P. (3) 54 260 — 123 Entities affiliated with Discovery Capital (4) — 106 — — Scott D. Grimes — 26 — — Lynne M. Laube — 14 — — Entities affiliated with Mark A. Johnson (5) 35 15 — 80 John Klinck 6 — — 13 David Adams 3 — — 7 (1) Consists of 159,207 shares of Series G’ redeemable convertible preferred stock issued to Aeroplan Holdings Europe Sàrl, 223,020 shares of Series G’ redeemable convertible preferred stock issued to Aimia EMEA Limited and 801,329 shares of common stock issued to Aimia EMEA Limited. (2) Consists of 27,988 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners V, L.P. (“PVP V”), 205,020 shares of Series G’ redeemable convertible preferred stock issued to PVP V, 64,038 warrants to purchase common stock issued to PVP V, 545 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners Entrepreneurs’ Fund V, L.L. (“PVP EF V”), 3,995 shares of Series G’ redeemable convertible preferred stock issued to PVP EF V, 1,247 warrants to purchase common stock issued to PVP EF V, 191 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners Founders’ Fund V, L.P. (“PVP FF V”), 1,404 shares of Series G’ redeemable convertible preferred stock issued to PVP FF V, 438 warrants to purchase common stock issued to PVP FF V, 280 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners Special Founders’ Fund V, L.P. (“PVP SFF V”), 2,050 shares of Series G’ redeemable convertible preferred stock issued to PVP SFF V and 641 warrants to purchase common stock issued to PVP SFF V. Polaris Venture Management Co. V, L.L.C. is a general partner of each of PVP V, PVP EF V, PVP FF V and PVP SFF V and may be deemed to have the sole voting and dispositive power over the shares held by PVP V, PVP EF V, PVP FF V and PVP SFF V. Bryce Youngren, a member of our board of directors, is a Managing Partner of Polaris Partners and may be deemed to share voting and dispositive power over the shares held by PVP V, PVP EF V, PVP FF V and PVP SFF V. (3) John V. Balen, a member of our board of directors, is a managing member of Canaan Partners VIII LLC, the general partner of Canaan VIII L.P. Mr. Balen does not have voting or investment power over any shares held directly by Canaan VIII L.P. (4) Consists of 95,272 shares of Series G’ redeemable convertible preferred stock issued to Discovery Opportunity Master Fund, Ltd. and 11,072 shares of Series G’ redeemable convertible preferred stock issued to Discovery Global Focus Master Fund, Ltd. (5) Consists of 15,045 shares of Series G’ redeemable convertible preferred stock issued to TTP Fund II, L.P., 29,005 shares of Series G redeemable convertible preferred stock purchased by TTV Ivy Holdings, LLC, 66,365 warrants to purchase common stock issued to TTV Ivy Holdings, LLC, 5,801 shares of Series G redeemable convertible preferred stock purchased by Mr. Johnson, and 13,273 warrants to purchase common stock issued to Mr. Johnson. TTV Capital is a provider of management services to TTP GP II, LLC, which is a general partner of TTP Fund II, L.P. TTV Capital is the manager of TTV Ivy Holdings Manager, LLC, which is the general partner of TTV Ivy Holdings, LLC. Mark A. Johnson, a member of our board of directors, is a member of each of TTP GP II, LLC and TTV Ivy Holdings Managers, LLC and holds the title of partner of TTV Capital, and may be deemed to share voting and dispositive power over the shares held by TTP Fund II L.P. and TTV Ivy Holdings, LLC. Agreements with Fidelity Information Services, LLC We are party to a reseller agreement with Fidelity Information Services LLC (“FIS”). Pursuant to the reseller agreement, FIS markets and sells our services to financial institutions that are current or potential customers of FIS in exchange for a revenue share percentage. We are also obligated to make milestone payments to FIS related to the integration and deployment of our solutions. Prior to our IPO, FIS was entitled to elect a member of our board of directors, who was Robert Legters until his resignation immediately prior to our IPO in February 2018. In May 2013, FIS purchased 397,515 shares of our Series E Stock. We also granted 10 -year performance-based warrants to purchase up to 644,365 shares of Series E Stock at an exercise price of $23.64 per share. The warrants were exercisable subject to the attainment of certain milestones related to the number of active accounts for which our solutions have been enabled with accelerated vesting upon an IPO. Since FIS did not participate in the convertible promissory note financing, their warrants to purchase preferred stock were converted to warrants to purchase common stock. The warrants vested upon the completion of our IPO in February 2018, resulting in a non-cash expense of $2.5 million based on the vesting-date fair value of our common stock underlying these warrants. Since the performance conditions were directly related to revenue-producing activities, we recognized this expense in FI Share and other third-party costs on our consolidated statement of operations. This expense is presented in other non-cash expenses on our consolidated statement of statement of cash flows. Refer to Note 10—Fair Value Measurement for additional information regarding the valuation of the performance-based warrants issued to FIS. Agreements with Aimia Inc. and Affiliated Entities In January 2014, we entered into a cooperation agreement with Aimia, which is a holder of our equity securities. As discussed in Note 12—Variable Interest Entity, Aimia agreed to terminate the cooperation agreement in June 2016 in exchange for $22.3 million of convertible promissory notes, resulting in Cardlytics, Inc. obtaining full control of Cardlytics UK. The net payable due to Aimia on June 30, 2016 totaled $5.7 million and was converted into a convertible promissory note. The termination of the cooperation agreement also resulted in a termination of the Working Capital Line of Credit. Refer to Note 5—Debt regarding the Working Capital Line of Credit and Aimia Notes.

VARIABLE INTEREST ENTITY

VARIABLE INTEREST ENTITY	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
VARIABLE INTEREST ENTITY	VARIABLE INTEREST ENTITY Cardlytics UK was operated through a cooperation agreement with Aimia whereby we and Aimia shared equally in cost and revenue related to the business in the U.K. On June 30, 2016, we and Aimia agreed to terminate this agreement, resulting in Cardlytics, Inc. obtaining full control of Cardlytics UK. While we maintained 100% equity ownership of Cardlytics UK, the cooperation agreement required that we establish a supervisory board, made up of two representatives from each of Cardlytics and Aimia, which is responsible for strategy and other approvals relating to the operations. As such, we and Aimia shared functional control over Cardlytics UK. Accordingly, Cardlytics UK was deemed to be a variable interest entity (“VIE”) while it was operated under the cooperation agreement. Subsequent to the termination of the cooperation agreement, Cardlytics UK is not considered a VIE as it is fully owned and controlled by Cardlytics, Inc. A VIE is an entity that has either a total equity investment that is insufficient to permit the entity to finance its activities without additional subordinated financial support, or whose equity investors lack the characteristics of a controlling financial interest (i.e., the ability to make significant decisions through voting rights and the right to receive the expected residual returns of the entity or the obligation to absorb the expected losses of the entity). A variable interest holder that has both (1) the power to direct the activities of the VIE that most significantly impact its economic performance and (2) either an obligation to absorb losses or a right to receive benefits that could potentially be significant to the VIE is referred to as the primary beneficiary and must consolidate the VIE. Cardlytics UK was deemed to be a VIE because we shared with Aimia the power to direct the activities that most significantly impacted Cardlytics UK’s economic performance, and Aimia did not hold any equity investment in Cardlytics UK. Due to the fact that we shared such decision making with Aimia, we individually did not have the characteristics of a primary beneficiary. However, we consolidated Cardlytics UK because (1) it was part of a related party group that included Aimia, (2) the related party group had the characteristics of a primary beneficiary and (3) we were most closely associated with Cardlytics UK. We concluded that we were most closely associated with Cardlytics UK because (1) merchants viewed Cardlytics UK as the primary obligor in the performance of marketing services with Aimia acting as a de facto agent on behalf of Cardlytics UK and (2) our software was used by Cardlytics UK in the performance of its services. We also had a disproportionate share of the economic risks when compared to our functional voting control as we incurred more than 50% of the expenses due to the absorption of 100% of the information technology and systems support related expenses for Cardlytics UK. There were no restrictions on the assets or liabilities of the VIE as a result of the cooperation agreement. The liabilities of the VIE were comprised mainly of short-term accrued expenses, and creditors had no recourse to our general credit or assets. Our conclusion that Cardlytics UK was a VIE was also partially reached due to the fact that Aimia was a related party. Our consolidated statements of operations includes the reimbursement of expense and allocation of revenue that are due to and due from Aimia pursuant to the agreement. Operating expense reimbursements and allocation of revenue less FI Share and third-party costs (recorded in FI Share and other third-party costs), are as follows (in thousands): Year Ended December 31, 2016 Operating expense reimbursements: Delivery costs $ 24 Sales and marketing expense 597 General and administrative expense 129 Allocation of revenue less FI Share and other third-party costs $ 1,223 Cardlytics UK’s effect on consolidated operating cash flows is a cash outflow of $0.6 million during 2016 . There were no material investing or financing cash flows associated with Cardlytics UK during 2016 .

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES FI Implementation Costs Agreements with certain FI partners require us to fund the development of specific enhancements, pay for certain implementation fees, or make milestone payments upon the deployment of our solution. Amounts paid to FI partners are included in deferred FI implementation costs on our consolidated balance sheets the earlier of when paid or earned and are amortized over the remaining term of the related contractual arrangements. Amortization is included in FI Share and other third-party costs on our consolidated statements of operations and is presented in amortization and impairment of deferred FI implementation costs on our consolidated statement of cash flows. Certain of these agreements provide for future reductions in FI Share due to the FI partner. These reductions in FI Share are recorded as a reduction to deferred implementation costs and also result in a cumulative adjustment to accumulated amortization. Reductions to FI Share in 2019 are expected to total $4.6 million . As of December 31, 2018 , there were no future scheduled amounts due to FI partners. One of our FI partners that we have made milestone payments to has experienced prolonged delays in implementing and supporting Cardlytics Direct. As a result, we wrote off deferred FI implementation costs totaling $0.8 million to FI Share and other third-party costs on our consolidated statements of operations in 2016 . The following table presents changes in deferred FI implementation costs (in thousands): December 31, 2016 2017 2018 Beginning balance $ 1,936 $ 8,451 $ 13,625 Deferred costs 8,205 10,900 9,250 Recoveries through FI Share — (4,100 ) (5,380 ) Amortization (876 ) (1,626 ) (1,618 ) Impairment (814 ) — — Ending balance $ 8,451 $ 13,625 $ 15,877 Payments to FI partners for enhancements not yet placed in service totaled $5.3 million as of December 31, 2018 . Future amortization, based on the amounts earned as of December 31, 2018 , exclusive of amounts expected to be recovered, is as follows (in thousands): Years Ending December 31, Amortization 2019 $ 3,744 2020 3,628 2021 3,245 Total $ 10,617 As a result of not meeting a minimum FI Share commitment in 2016, we were required to pay an FI partner $2.6 million in March 2017 . This shortfall was accrued in 2016 and recorded within FI Share and other third-party costs on our consolidated statement of operations. We have a minimum FI Share commitment with a certain FI partner totaling $10.0 million over a 12-month period following the completion of certain milestones, which were not met as of December 31, 2018. Any expected shortfall will be accrued during the 12-month period following the completion of the milestones. Operating Leases We lease office and apartment space and office equipment under non-cancellable operating lease agreements expiring on various dates through April 2026. For leases that contain rent escalation or rent concession provisions, we record the total rent expense during the lease term on a straight-line basis over the term of the lease. On our consolidated balance sheets, the current portion of deferred rent is included in accrued liabilities and the long-term portion is included within deferred liabilities. Rent expense during 2016 , 2017 and 2018 totaled $2.9 million , $3.0 million and $3.0 million , respectively. In August 2013, we entered into a lease of 130 months for our new corporate headquarters in Atlanta, Georgia. The facility was delivered to us in July 2014 and provides 76,880 square feet of office space. The lease contains a $3.8 million tenant improvement allowance that is included in deferred rent and amortized as a reduction to rent expense over the lease term. Minimum lease payments under the agreement total $16.0 million . In July 2015, we entered into a lease of 60 months to expand our existing data center space located in Atlanta, Georgia. Minimum lease payments under the agreement total $2.3 million . In December 2016, we entered into a lease of 40 months for an office in Victoria, London to provide 5,295 square feet of office space. Minimum lease payments under the agreement total £0.8 million . As of December 31, 2018 , future minimum lease payments under non-cancellable operating leases are as follows (in thousands): Years Ending December 31, Minimum Lease Payments 2019 $ 2,706 2020 2,089 2021 1,654 2022 1,703 2023 1,755 Thereafter 2,418 Total $ 12,325 Litigation From time to time, we may become involved in legal actions arising in the ordinary course of business including, but not limited to, intellectual property infringement and collection matters. We make assumptions and estimates concerning the likelihood and amount of any potential loss relating to these matters using the latest information available. We record a liability for litigation if an unfavorable outcome is probable and the amount of loss or range of loss can be reasonably estimated. If an unfavorable outcome is probable and a reasonable estimate of the loss is a range, we accrue the best estimate within the range. If no amount within the range is a better estimate than any other amount, we accrue the minimum amount within the range. If an unfavorable outcome is probable but the amount of the loss cannot be reasonably estimated, we disclose the nature of the litigation and indicates that an estimate of the loss or range of loss cannot be made. If an unfavorable outcome is reasonably possible and the estimated loss is material, we disclose the nature and estimate of the possible loss of the litigation. We do not disclose information with respect to litigation where an unfavorable outcome is considered to be remote or where the estimated loss would not be material. Based on current expectations, such matters, both individually and in the aggregate, are not expected to have a material adverse effect on our liquidity, results of operations, business or financial condition. Letters of Credit In connection with the lease of the new corporate headquarters, we executed a $2.5 million irrevocable letter of credit on April 1, 2014. In December 2016, upon transitioning our operating bank accounts to a new financial institution, we replaced our existing irrevocable letter of credit with a new $2.0 million irrevocable letter of credit, which reduced to $1.5 million in May 2017 and $1.0 million in May 2018.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE Diluted net loss per share is the same as basic net loss per share for 2016 , 2017 and 2018 because the effects of potentially dilutive items were anti-dilutive, given our net loss during these periods. The following securities have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive (in thousands): December 31, 2016 2017 2018 Redeemable convertible preferred stock: Series A-R 1,857 1,857 — Series B-R 2,247 2,247 — Series C-R 1,508 1,508 — Series D-R 1,396 1,396 — Series E-R 795 795 — Series F-R 1,199 1,199 — Series G — 346 — Series G’ — 1,296 — Common stock options 2,137 2,514 1,774 Common stock warrants 1,227 1,245 867 Common stock warrants issuable pursuant to Series G Stock financing — 547 — Redeemable convertible preferred stock warrants 110 110 — Restricted stock units — — 381 Restricted securities units 53 37 — Convertible promissory notes 2,734 — — Common stock issuable pursuant to the ESPP — — 36

SEGMENTS

SEGMENTS	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
SEGMENTS	SEGMENTS As of December 31, 2018 , we have three operating segments: Cardlytics Direct in the U.S. and U.K. and Other Platform Solutions, as determined by the information that both our Chief Executive Officer and President and Chief Operating Officer, who we consider our chief operating decision makers, use to make strategic goals and operating decisions. Our Cardlytics Direct operating segments in the U.S. and U.K. represent our proprietary native bank advertising channels and are aggregated into one reportable segment given their similar economic characteristics, nature of service, types of customers and method of distribution. Our Other Platform Solutions enabled marketers and marketing service providers to leverage the power of purchase intelligence outside the bank channel. We have shifted the substantial majority of our efforts and resources to support the growth of Cardlytics Direct. As a result, we do not expect to generate substantial, if any, revenue from Other Platform Solutions for the foreseeable future. Revenue can be directly attributable to each segment. With the exception of a non-cash equity expense and the amortization and impairment of deferred FI implementation costs, FI Share is also directly attributable to each segment. Our chief operating decision makers allocate resources to, and evaluate the performance of, our operating segments based on revenue and adjusted contribution. The accounting policies of each of our reportable segments are the same as those described in the summary of significant accounting policies. The following table provides information regarding our reportable segments (in thousands): Year Ended December 31, 2016 2017 2018 Cardlytics Direct: Adjusted contribution (2)(3) $ 41,374 $ 55,184 $ 69,364 Plus: FI Share and other third-party costs (1) 56,415 67,207 79,959 Revenue $ 97,789 $ 122,391 $ 149,323 Other Platform Solutions: Adjusted contribution $ 6,852 $ 3,560 $ 86 Plus: FI Share and other third-party costs (1) 8,180 4,414 1,275 Revenue $ 15,032 $ 7,974 $ 1,361 Total: Adjusted contribution (2)(3) $ 48,226 $ 58,744 $ 69,450 Plus: FI Share and other third-party costs (1) 64,595 71,621 81,234 Revenue $ 112,821 $ 130,365 $ 150,684 (1) FI Share and other third party costs presented above excludes a non-cash equity expense and amortization and impairment of deferred FI implementation costs, which are detailed below in our reconciliation of GAAP loss before income taxes to non-GAAP adjusted contribution. (2) Adjusted contribution includes the impact of an accrued expense totaling $2.6 million during 2016 related to shortfall in meeting a minimum FI Share commitment. There was no corresponding accrued expense during 2017 and 2018. (3) Adjusted contribution includes the impact of a $0.8 million gain during 2018 related to the renewal of our agreement with Lloyds, which contains certain amendments that are retroactively applied as of January 1, 2018. Adjusted Contribution Adjusted contribution represents our revenue less FI Share and other third-party costs excluding a non-cash equity expense included in FI Share and amortization and impairment of deferred FI implementation costs. During the first quarter of 2018, we refined our definition of adjusted contribution used by our chief operating decision makers to exclude the impact of a non-cash charge related to the issuance of equity to an FI partner and the impact of amortization and impairment of deferred FI implementation costs. We believe these changes are warranted and appropriate since these investments are expected to yield meaningful long-term relationships with our FI partners and provide incentive for our FI partners to invest in the user interfaces that complement our platform. We have recast all historical disclosures of adjusted contribution for the periods presented. The following table presents a reconciliation of loss before income taxes presented in accordance with GAAP to adjusted contribution (in thousands): Year Ended December 31, 2016 2017 2018 Adjusted contribution $ 48,226 $ 58,744 $ 69,450 Minus: Non-cash equity expense included in FI Share (1) — — 2,519 Amortization and impairment of deferred FI implementation costs (1) 1,690 1,626 1,618 Delivery costs 6,127 7,012 10,632 Sales and marketing expense 31,261 31,927 41,878 Research and development expense 13,902 12,150 16,210 General and administration expense 21,355 20,100 34,228 Depreciation and amortization expense 4,219 3,028 3,282 Termination of U.K. agreement expense 25,904 — — Total other expense 19,464 2,542 12,125 Loss before income taxes $ (75,696 ) $ (19,641 ) $ (53,042 ) (1) Non-cash equity expense included in FI Share and amortization and impairment of deferred FI implementation costs are excluded from FI Share and other third party costs, which is shown above in our reconciliation of GAAP revenue to non-GAAP adjusted contribution. The following tables provides geographical information (in thousands): Year Ended December 31, 2016 2017 2018 Revenue: United States $ 100,590 $ 113,509 $ 131,563 United Kingdom 12,231 16,856 19,121 Total $ 112,821 $ 130,365 $ 150,684 December 31, 2017 2018 Property and equipment: United States $ 6,813 $ 9,794 United Kingdom 506 436 Total $ 7,319 $ 10,230 Capital expenditures within the United Kingdom were $0.3 million and less than $0.1 million during 2017 and 2018 , respectively.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements. Actual results could differ from these estimates. Significant items subject to such estimates and assumptions include revenue recognition, internal-use software development costs, income taxes, stock-based compensation, derivative instruments, income tax valuation allowance, contingencies and changes in fair value of our convertible promissory notes. We base our estimates on historical experience and also on assumptions that we believe are reasonable. Changes in facts or circumstances may cause us to change our assumptions and estimates in future periods and it is possible that actual results could differ from our current or revised future estimates.
Foreign Currency	Foreign Currency The functional currency of our foreign wholly owned subsidiaries is the local currency. We translate the financial statements of these subsidiaries into U.S. dollars each reporting period for purposes of consolidation. Assets and liabilities are translated at the period-end currency exchange rates, certain equity accounts are translated at historical exchange rates and income and expense amounts are translated at average currency exchange rates in effect for the period. The effect of these translation adjustments is reported in a separate component of stockholders’ deficit titled accumulated other comprehensive income. We are also subject to gains and losses from foreign currency denominated transactions and the remeasurement of foreign currency denominated balance sheet accounts, both of which are included in other expense, net in the accompanying consolidated statements of operations.
Revenue	Revenue We generate revenue through the sale of two categories of solutions that leverage our intelligence platform: (1) our proprietary native banking channel, Cardlytics Direct and (2) our Other Platform Solutions. We have generated substantially all of our revenue from sales of Cardlytics Direct since inception. Our Other Platform Solutions enabled marketers and marketing service providers to leverage the power of purchase intelligence outside the bank channel. We have shifted the majority of our efforts and resources to support the growth of Cardlytics Direct. As a result, we do not expect to generate substantial, if any, revenue from Other Platform Solutions for the foreseeable future. Cardlytics Direct Cardlytics Direct is our proprietary native bank advertising channel that enables marketers to reach consumers through their trusted and frequently visited online and mobile banking channels. Working with the marketer, we design a campaign that targets customers based on their purchase history. The consumer is offered an incentive to make a purchase from the marketer within a specified period. We use a portion of the fees that we collect from marketers to provide these consumer incentives to our FIs’ customers after they make qualifying purchases ("Consumer Incentives"). Leveraging our powerful predictive analytics, we are able to create compelling Consumer Incentives that have the potential to increase return on advertising spend for marketers. We also pay our FI partners an FI Share. Cardlytics Direct is priced predominantly in two ways: (1) Cost per Served Sale (“CPS”), and (2) Cost per Redemption (“CPR”). In 2016 , 2017 and 2018 , CPS represented 67% , 66% and 68% of our revenue from Cardlytics Direct. • CPS . Our primary pricing model is CPS, which we created to meet the media buying preferences of marketers. We generate revenue by charging a percentage, which we refer to as the CPS Rate, of all purchases from the marketer by consumers (1) who are served marketing and (2) subsequently make a purchase from the marketer during the campaign period, regardless of whether consumers select the marketing and thereby becomes eligible to earn the applicable Consumer Incentive. We set CPS Rates for marketers based on our expectation of the marketer’s return on spend for the relevant campaign. Additionally, we set the amount of the Consumer Incentives payable for each campaign based on our estimation of our ability to drive incremental sales for the marketer. We seek to optimize the level of Consumer Incentives to retain a greater portion of billings. However, if the amount of Consumer Incentives exceeds the amount of billings that we are paid by the applicable marketer we are still responsible for paying the total Consumer Incentive. This has occurred infrequently and has been immaterial in amount for each of the periods presented. • CPR . Our initial pricing model is CPR, where marketers specify and fund the Consumer Incentive and pay us a separate negotiated, fixed marketing fee, which we refer to as the CPR Fee, for each purchase that we generate. We generate revenue if the consumer (1) is served marketing, (2) selects the marketing and thereby becomes eligible to earn the applicable Consumer Incentive and (3) makes a qualifying purchase from the marketer during the campaign period. We set the CPR Fee for marketers based on our estimation of the marketers’ return on spend for the relevant campaign. The CPR Fee is either a percentage of qualifying purchases or a flat amount. Revenue Recognition We recognize revenue in accordance with Accounting Standards Codification (“ASC”) Topic 605, Revenue Recognition , on a transaction when all of the following conditions have been satisfied: • persuasive evidence of an agreement exists; • the service has been provided to the customer; • fees are fixed or determinable; and • the collection of the fees is reasonably assured. If any of these criteria are not met, revenue recognition is deferred until such time that all of the criteria are met. Our deferred revenue is primarily comprised of payments received in advance for Cardlytics Direct marketing campaigns. We sell our solutions by entering into agreements directly with marketers or their marketing agencies. The agreements state the terms of the arrangement, the agreed upon fee and, with respect to Cardlytics Direct, the fixed period of time the offers will be available to FI customers. Persuasive evidence of an arrangement is considered to exist and the fee is considered fixed and determinable upon the execution of an insertion order. With respect to our Cardlytics Direct service, the service is deemed to have been provided to the marketer as FIs’ customers make qualifying purchases during the marketing campaign term. With respect to Other Platform Solutions, the service is deemed to have been provided (1) for non-managed service campaigns, when we deliver the purchase intelligence to the marketer and (2) for managed service campaigns, when the digital advertising impressions contemplated by the campaign have been served to targeted consumers. We determine collectability upfront and on an on-going basis by performing credit evaluations and monitoring our marketers’ accounts receivable balances. Gross/Net Consideration We evaluate the appropriateness of revenue reporting on a gross or net basis by considering the indicators outlined within ASC Topic 605-45, Revenue Recognition—Principal Agent Considerations and ASC Topic 605-50, Customer Payments and Incentives . We consider the nature of the costs and risks associated with the indicators present in evaluating the substance of an arrangement. We consider the relative strength of each indicator and certain factors may be assessed to carry more weight in the evaluation.
Consumer Incentives	Consumer Incentives Cardlytics Direct is our proprietary native bank advertising channel that enables marketers to reach consumers via their trusted and frequently visited online and mobile banking channels as well as email. Working with the marketer, we design a campaign that targets customers based on their purchase history. The consumer is offered an incentive to make a purchase from the marketer within a specified period, which we refer to as Consumer Incentives. We use a portion of the fees that we collect from marketers to provide these Consumer Incentives to our FIs’ customers after they make qualifying purchases. We report our revenue on our consolidated statements of operations net of Consumer Incentives. We do not provide the goods or services that are purchased by our FIs’ customers from the marketers to which the Consumer Incentives relate. Accordingly, the marketer is deemed to be the principal in the relationship with the customer and, therefore, the Consumer Incentive is deemed to be a reduction in the purchase price paid by the customer for the marketer’s goods or services. While we are responsible for remitting Consumer Incentives to our FI partners for further payment to their customers, we function solely as an agent of marketers in these arrangements. Accounts receivable is recorded at the amount of gross billings to marketers, net of allowances, for the fees and Consumer Incentives that we are responsible to collect. Our accrued liabilities also include the amount of Consumer Incentives due to FI partners. As a result, accounts receivable and accrued liabilities may appear large in relation to revenue, which is reported on a net basis.
FI Share and Other Third-Party Costs	FI Share and Other Third-Party Costs We report our revenue on our consolidated statements of operations gross of FI Share. FI Share is included in FI Share and other third-party costs in our consolidated statements of operations, rather than as a reduction of revenue, because we and not our FI partners act as the principal in our arrangements with marketers. We are responsible for the fulfillment and acceptability of the services purchased by marketers. We also have latitude in establishing the price of our services, have discretion in supplier selection and earn variable amounts. FI partners only supply consumer purchase data and digital marketing space and have no involvement in the marketing campaigns or contractual relationship with marketers. We incurred media costs in connection with the delivery of managed services with respect to our Other Platform Solutions. We reported our revenue on our consolidated statements of operations gross of media costs. Media costs were included in FI Share and other third-party costs in our consolidated statements of operations, rather than as a reduction of revenue, because we and not exchanges or digital publishers acted as the principal in our arrangements with marketers. FI Share and Other Third-Party Costs FI Share and other third-party costs consist primarily of the FI Share that we pay our FI partners, media and data costs, and through June 30, 2016, allocation of revenue in the U.K. to Aimia as discussed in Note 12—Variable Interest Entity. FI Share and other third-party costs also include the amortization and impairment of implementation costs incurred pursuant to our agreements with certain FI partners, any incremental costs due to FIs as part of FI Share commitments, as well as a non-cash expense related to the vesting of warrants issued to an FI partner that accelerated upon the consummation of our IPO. With respect to Cardlytics Direct, we pay FI Share based on the gross billings to marketers less any Consumer Incentives that we pay to our FI partners and certain third-party data costs. To the extent that we use a specific FI customer’s anonymized purchase data in the delivery of our Other Platform Solutions, we pay the applicable FI partner an FI Share calculated based on the relative contribution of the data provided by the FI partner to the overall delivery of the services. Delivery Costs Delivery costs consist primarily of personnel-related costs of our campaign, data operations and production support teams, including salaries, benefits, bonuses and payroll taxes, as well as stock-based compensation expense. Delivery costs also include hosting facility costs, internally developed and purchased or licensed software costs, outsourcing costs and professional services costs. Accounts Receivable Accounts receivable are carried at the original invoiced amount less an allowance for doubtful accounts, determined based on the probability of future collection. When we become aware of circumstances that may decrease the likelihood of collection, we record a specific allowance against amounts due, which reduces the receivable to the amount that we believe will be collected. For all other accounts receivable, we determine the adequacy of the allowance based on historical loss patterns, the number of days that billings are past due and an evaluation of the potential risk of loss associated with specific accounts. The following table presents changes in the allowance for doubtful accounts (in thousands): Year Ended December 31, 2016 2017 2018 Beginning balance $ 746 $ 653 $ 105 Bad debt expense 1,100 73 130 Write-offs, net of recoveries (1,193 ) (621 ) (66 ) Ending balance $ 653 $ 105 $ 169 Unbilled receivables were $0.5 million , $0.1 million and $0.4 million as of December 31, 2016 , 2017 and 2018 , respectively. An unbilled receivable represents revenue earned and recognized from customer activity that was not billed prior to the end of the reporting period. Unbilled receivables are included in accounts receivable, net on our consolidated balance sheets.
Concentration of Risk	Concentrations of Risk Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents and accounts receivable. Our cash and cash equivalents are held with three financial institutions, which we believe are of high credit quality. We believe that our accounts receivable credit risk exposure is limited as a result of being diversified among a large number of marketers segregated by both geography and industry. Historically, we have not experienced significant write-downs of our accounts receivable. No marketer represented a significant concentration of our accounts receivable as of December 31, 2017 or December 31, 2018 . No marketer accounted for over 10% of revenue during 2016 , 2017 or 2018 . Our business is substantially dependent on a limited number of FI partners. We require participation from our FI partners in Cardlytics Direct and access to their purchase data in order to offer our solutions to marketers and their agencies. We must have FI partners with a sufficient number of customers and levels of customer engagement to ensure that we have robust purchase data and marketing space to support a broad array of incentive programs for marketers. Our agreements with a substantial majority of our FI partners have terms of three to five years but are generally terminable by the FI partner on 90 days or less prior notice. If an FI partner terminates its agreement with us, we would lose that FI as a source of purchase data and digital banking customers. A new FI partner launched the Cardlytics Direct program in November 2018 and accounted for 17% of our aggregate FI Share during the fourth quarter of 2018. During 2016 , 2017 , 2018 and the fourth quarter of 2018 , our largest FI partner in the U.S. accounted for approximately 64% , 63% , 64% and 55% of FI Share, respectively. During 2016 , 2017 , 2018 and the fourth quarter of 2018 , an FI partner in the U.K. accounted for 10% , 12% , 9% and 8% of FI Share, respectively. No other FI partners accounted for over 10% of FI Share during 2016 , 2017 , 2018 or the fourth quarter of 2018.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents consist of cash held in checking accounts, upon which we earn up to a 1.1% annual rate of interest as of December 31, 2018 . Restricted cash primarily represents deposits held in an account controlled by our lender as additional security for our payment obligations under our 2018 Term Loan, upon which we earn a 1.4% annual rate of interest as of December 31, 2018 . Refer to Note 5—Debt for additional information regarding our 2018 Term Loan. Cash, cash equivalents and restricted cash as presented on our consolidated statements of cash flows consists of the following (in thousands): December 31, 2016 2017 2018 Cash and cash equivalents $ 22,838 $ 21,262 $ 39,623 Restricted cash 130 — 20,247 Cash, cash equivalents and restricted cash $ 22,968 $ 21,262 $ 59,870
Property and Equipment	Property and Equipment Property and equipment are stated at cost. Expenditures for maintenance and repairs are expensed as incurred, while betterments that materially extend the life of an asset are capitalized. The cost of assets sold, retired or otherwise disposed of, and the related accumulated depreciation, are eliminated from the accounts and any resulting gain or loss is recognized. Depreciation of property and equipment is determined using the straight-line method over the estimated useful lives of the applicable assets, which are as follows: Computer equipment: 2–3 years Furniture and fixtures: 5 years Leasehold improvements: Lesser of estimated useful life or life of the lease
Intangible assets	Intangible Assets Intangible assets are recorded at cost and consist of costs incurred for software patent applications. We received approval for three patents in 2013 and one patent in 2018 and began amortizing the costs of obtaining these patents over the estimated remaining lives of the patents. If a patent application is rejected or if we abandon efforts to obtain a new patent, all deferred patent costs are expensed immediately. Deferred patent costs related to patents for which we have not yet obtained approval totaled $0.4 million and $0.2 million as of December 31, 2017 and 2018 , respectively. Based on deferred patent costs as of December 31, 2018 , the related amortization expense will be less than $0.1 million in each of the next five years. Intangible assets are as follows (in thousands):
Internal Use Software	Internal-Use Software Development Costs Capitalized software development costs consist of costs incurred in the development of internal-use software, primarily associated with the development and enhancement of our offer management system and offer placement system. We capitalize the costs of software developed or obtained for internal use in accordance with ASC Topic 350-40, Internal Use Software . We begin to capitalize our costs upon completion of the preliminary project stage. We consider the preliminary project stage to be complete and the application development stage to have begun when preliminary development efforts are successfully completed, management has authorized and committed project funding and it is probable that the project will be completed and the software will be used as intended. These costs are amortized on a straight-line basis over the estimated useful life of the related asset, generally estimated to be five years. Costs incurred in the preliminary project stage and post-implementation operation stages are expensed as incurred and recorded in research and development expense on our consolidated statements of operations.
Impairment of long-lived assets	Impairment of Long-Lived Assets We review long-lived assets and intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be fully recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of the assets to the undiscounted future net cash flows expected to be generated by the assets. If such assets are not considered to be recoverable, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the fair value of the assets.
Debt Issuance Costs	Debt Issuance Costs Costs incurred to obtain loans, other than lines of credit, are recorded as a reduction of the carrying amount of the related liability and amortized over the applicable loans’ life using the effective interest method. Costs incurred to obtain lines of credit are capitalized and included in other long-term assets on our consolidated balance sheets and amortized ratably over the term of the arrangement. Costs incurred to obtain loans for which we have elected the fair value option are expensed upon the issuance of the loan and recorded within general and administrative expense on our consolidated statements of operations.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs consist of incremental costs directly attributable to equity offerings. Deferred offering costs are included in other long-term assets on our consolidated balance sheets. Upon completion of an offering, these amounts are offset against the proceeds of the offering.
Reduction In Force	Reduction in Force In 2016, we announced a strategic shift to rebalance our resources and put us on a faster path to potential profitability. This workforce reduction plan resulted in $1.3 million of charges, consisting primarily of severance and medical benefits, recognized in 2016 when the extent of our action was determined and could be estimated. All severance and medical benefits were paid to former employees as of December 31, 2016. Additionally, vested stock options of affected employees were cancelled and re-granted with similar terms, but with exercise periods of up to two years, resulting in stock compensation expense of less than $0.1 million .
Advertising	Advertising We expense advertising costs as incurred. These costs are included in sales and marketing expense on our consolidated statements of operations. Advertising costs include direct marketing costs such as print advertisements, market research, direct mail, public relations and trade show expenses and totaled $0.9 million , $0.7 million and $0.9 million in 2016 , 2017 and 2018 , respectively.
Research and Development Costs	Research and Development Costs Research and development expense consists primarily of personnel costs of our information technology ("IT") engineering, IT architecture and product development teams, including salaries, benefits, bonuses, stock-based compensation and payroll taxes. Research and development expense also includes outsourcing costs, software licensing costs, professional fees and travel expenses.
Stock-Based Compensation	Stock-Based Compensation We measure and recognize compensation expense for all stock options and restricted stock units based on the fair value of the award on the grant date. We use the Black-Scholes option pricing model to estimate the fair value of stock option awards. The fair value of RSUs is determined based on the value of the underlying common stock on the grant date. The fair value is recognized as expense over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis when the only condition to vesting is continued service. Forfeitures are accounted for when they occur. We recognize the fair value of stock options which contain performance conditions based upon the probability of the performance conditions being met. We have not issued awards where vesting is subject to a market condition; however, if we were to grant such awards in the future, recognition would be based on the derived service period. Expense for awards with performance conditions are estimated and adjusted on a quarterly basis based upon our assessment of the probability that the performance condition will be met. Refer to Note 6—Stock-based Compensation for additional information regarding our specific award plans and estimates and assumptions used to determine fair value.
Redeemable Convertible Preferred Stock Warrant Liability	Redeemable Convertible Preferred Stock Warrant Liability Warrants to purchase shares of our redeemable convertible preferred stock are accounted for as derivative liabilities in accordance with ASC Topic 815, Derivatives and Hedging due to the terms of the warrants and related agreements. We have determined that these warrants do not meet the scope exception of a contract indexed to our stock because of fair value protections contained in agreements governing our redeemable convertible preferred stock as described in Note 8—Redeemable Convertible Preferred Stock. We record preferred stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses on our statements of operations.
Common Stock Warrant Liability	Common Stock Warrant Liability In connection with the Series G Stock financing, we issued warrants to purchase shares of our common stock that are accounted for as liabilities in accordance with ASC Topic 480, Distinguishing Liabilities From Equity due to the terms of the warrants and related agreements. We record these common stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses in our statements of operations
Fair Value of Financial Instruments	Fair Value of Financial Instruments When required by GAAP, assets and liabilities are reported at fair value on our consolidated financial statements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Valuation inputs are arranged in a hierarchy that consists of the following levels: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. • Level 2 inputs are inputs other than Level 1 inputs such as quoted prices for similar assets or liabilities; quoted prices in markets with insufficient volume or infrequent transactions (less active markets); or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3 inputs are unobservable inputs for the asset or liability. Our nonfinancial assets that we recognize or disclose at fair value on our consolidated financial statements on a nonrecurring basis include property and equipment, intangible assets, capitalized software development costs and deferred FI implementation costs. The fair values for these assets are evaluated when events or changes in circumstances indicate the carrying value may not be recoverable. Preferred Stock Warrants Outstanding warrants to purchase shares of our redeemable convertible preferred stock are accounted for as derivative liabilities in accordance with ASC Topic 815, Derivatives and Hedging (“ASC 815”) due to the terms of the warrants and related agreements. We have determined that these warrants do not meet the scope exception of a contract indexed to our stock because of fair value protections contained in agreements governing our redeemable convertible preferred stock. We record preferred stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses on our consolidated statements of operations. Upon the consummation of our IPO, all warrants to purchase shares of our redeemable convertible preferred stock were converted to warrants to purchase shares of our common stock. Refer to Note 10—Fair Value Measurement for additional information regarding the valuation of warrants to purchase shares of our redeemable convertible preferred stock. Common Stock Warrants Issued in Connection with the Series G Stock Financing In connection with the Series G Stock financing, we issued warrants to purchase shares of our common stock that are accounted for as liabilities in accordance with ASC Topic 480, Distinguishing Liabilities From Equity due to the terms of the warrants and related agreements. We record these common stock warrant liabilities on our consolidated balance sheets at their fair value. We record the changes in fair value of such instruments as non-cash gains or losses on our consolidated statements of operations. In August 2018, we issued warrants to purchase 792,434 shares of common stock at an exercise price of $0.0004 per share to the cash investors of our Series G financing, pursuant to our Series G stock purchase agreement. The warrants had a valuation of $15.3 million upon issuance and were subsequently exercised, resulting in the issuance of 792,434 shares of our common stock. Refer to Note 10—Fair Value Measurement for additional information regarding the valuation of the warrants issued in connection with the Series G Stock financing. Convertible Promissory Notes The redemption features included in the terms of the convertible promissory notes were determined to be derivative liabilities as a result of a significant discount within the redemption features for the note holders. Embedded derivatives that are not clearly and closely related to the host contract are required to be bifurcated and recorded at fair value unless the fair value option is elected on the host contract. Under the fair value option, bifurcation of the embedded derivative is not necessary as all related gains or losses on the host contract and derivative will be reflected on the consolidated statements of operations. We elected the fair value option for the convertible promissory notes upon their issuance. The convertible promissory notes are measured at fair value using unobservable inputs that required a high level of judgment, and are therefore classified as Level 3. In May 2017, we issued and sold shares of Series G redeemable convertible preferred stock, which resulted in the conversion of the convertible promissory notes into either shares of our common stock or shares of our Series G’ Stock. Refer to Note 10—Fair Value Measurement for additional information regarding the valuation of the convertible promissory notes.
Income Taxes	Income Taxes Income taxes are accounted for using the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective income tax bases, and operating loss and tax credit carryforwards. Valuation allowances are provided when we determine that it is more likely than not that all of, or a portion of, deferred tax assets will not be utilized in the future. Significant judgment is required in determining any valuation allowance recorded against deferred tax assets. In assessing the need for a valuation allowance, we consider all available evidence, including past operating results, estimates of future taxable income and the feasibility of tax planning strategies. In the event that we change our determination as to the amount of deferred tax assets that can be realized, we will adjust our valuation allowance with a corresponding impact to the provision for income taxes in the period in which such determination is made. Estimates of future taxable income are based on assumptions that are consistent with our plans. Assumptions represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. If actual amounts differ from our estimates, the amount of our tax expense and liabilities could be materially impacted. We have recorded a full valuation allowance related to our net deferred tax assets due to the uncertainty of the ultimate realization of the future benefits of those assets. We recognize the tax effects of an uncertain tax position only if it is more likely than not to be sustained based solely on its technical merits as of the reporting date, and then, only in an amount more likely than not to be sustained upon review by the tax authorities. Where applicable, we classify associated interest and penalties as income tax expense. The total amounts of interest and penalties were not material. We consider many factors when evaluating and estimating our tax positions and tax benefits, which may require periodic adjustments and which may not accurately anticipate actual outcomes. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (“Tax Act”) was signed into law making significant changes to the Internal Revenue Code of 1986, as amended (“IRC”). Changes include, but are not limited to, a corporate tax rate decrease to 21% effective for tax years beginning after December 31, 2017. This change in tax rate resulted in a reduction in our net U.S. deferred tax assets, which was fully offset by a reduction in our valuation allowance. The other provisions of the Tax Act, including the one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings, did not have a material impact on our financial statements.
New Accounting Pronouncements	Recently Adopted Accounting Pronouncements In May 2017, the FASB issued ASU 2017-09, Scope of Modification Accounting , which amends the scope of modification accounting for share-based payment arrangements, provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under ASC Topic 718, Compensation—Stock Compensation . For all entities, the ASU is effective prospectively for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We adopted this ASU on January 1, 2018 and it did not have an impact on our consolidated financial statements. Recently Issued Accounting Pronouncements In May 2014, the FASB issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606). ASU 2014-09 supersedes the recognition guidance in ASC Topic 605 and most industry specific revenue guidance and requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which it expects to be entitled in exchange for those goods or services. In addition, this ASU requires disclosures of the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. This guidance permits the use of either the retrospective or modified retrospective transition method. For public entities, this ASU is effective for fiscal years beginning after December 15, 2017, including interim periods within those annual periods. For non-public entities, this ASU is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. We have made the election to use the extended transition period for complying with new or revised accounting standards under Section 102(b)(1) of the Jumpstart Our Business Startups Act of 2012 ("JOBS Act"), therefore we will be required to apply this ASU for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. We adopted this guidance on January 1, 2019 using the modified retrospective approach. We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which is intended to enhance the reporting model for financial instruments to provide users of financial statements with more decision-useful information. This ASU requires equity investments to be measured at fair value with changes in fair values recognized in net earnings, (public entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes), simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment and eliminates the requirement to disclose fair values, the methods and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost. This ASU also clarifies that management should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale debt securities in combination with other deferred tax assets. For public business entities, this ASU is effective for fiscal years beginning after December 15, 2017, including interim periods within those annual periods. For non-public business entities, this ASU is effective for fiscal years beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. Early adoption is permitted. We have made the election to use the extended transition period for complying with new or revised accounting standards under Section 102(b)(1) of the JOBS Act, therefore we will be required to apply this ASU for annual reporting periods beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. We adopted this guidance on January 1, 2019. We do not expect the adoption of this ASU to have a material impact on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , which supersedes ASC Topic 840, Leases . The ASU does not significantly change the lessees’ recognition, measurement and presentation of expenses and cash flows from the previous accounting standard. The ASU’s primary change is the requirement for lessee entities to recognize a lease liability for payments and a right of use asset representing the right to use the leased asset during the term on operating lease arrangements. Lessees are permitted to make an accounting policy election to not recognize the asset and liability for leases with a term of twelve months or less. Lessors’ accounting under the ASU is largely unchanged from the previous accounting standard. In addition, the ASU expands the disclosure requirements of lease arrangements. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842) - Targeted Improvements , which provides the option of applying the requirements of the new lease standard in the period of adoption with no restatement to comparative periods. For public entities, this ASU is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. For non-public entities, this ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We have made the election to use the extended transition period for complying with new or revised accounting standards under Section 102(b)(1) of the JOBS Act, therefore we will be required to adopt this ASU for annual reporting periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Although we are currently evaluating the impact of this guidance on our consolidated financial statements, we expect that most of our operating lease commitments will be recognized as operating lease liabilities and right-of-use assets upon adoption of the new guidance.

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of allowance for doubtful accounts	The following table presents changes in the allowance for doubtful accounts (in thousands): Year Ended December 31, 2016 2017 2018 Beginning balance $ 746 $ 653 $ 105 Bad debt expense 1,100 73 130 Write-offs, net of recoveries (1,193 ) (621 ) (66 ) Ending balance $ 653 $ 105 $ 169
Schedule of cash and cash equivalents	Cash, cash equivalents and restricted cash as presented on our consolidated statements of cash flows consists of the following (in thousands): December 31, 2016 2017 2018 Cash and cash equivalents $ 22,838 $ 21,262 $ 39,623 Restricted cash 130 — 20,247 Cash, cash equivalents and restricted cash $ 22,968 $ 21,262 $ 59,870
Schedule of restricted cash	Cash, cash equivalents and restricted cash as presented on our consolidated statements of cash flows consists of the following (in thousands): December 31, 2016 2017 2018 Cash and cash equivalents $ 22,838 $ 21,262 $ 39,623 Restricted cash 130 — 20,247 Cash, cash equivalents and restricted cash $ 22,968 $ 21,262 $ 59,870
Schedule of property and equipment, useful life	Depreciation of property and equipment is determined using the straight-line method over the estimated useful lives of the applicable assets, which are as follows: Computer equipment: 2–3 years Furniture and fixtures: 5 years Leasehold improvements: Lesser of estimated useful life or life of the lease Significant components of property and equipment are as follows (in thousands): December 31, 2017 2018 Computer equipment $ 10,827 $ 16,284 Leasehold improvements 5,399 5,573 Furniture and fixtures 824 913 Construction in progress — 65 Property and equipment, gross 17,050 22,835 Less accumulated depreciation (9,731 ) (12,605 ) Property and equipment, net $ 7,319 $ 10,230
Schedule of indefinite-lived intangible assets	Intangible assets are as follows (in thousands): December 31, 2017 2018 Deferred patent costs, gross $ 563 $ 417 Less accumulated amortization (35 ) (47 ) Deferred patent costs, net $ 528 $ 370 Capitalized software development costs are as follows (in thousands): December 31, 2017 2018 Capitalized software development costs, gross $ 1,487 $ 2,826 Less accumulated amortization (1,054 ) (1,201 ) Capitalized software development costs, net $ 433 $ 1,625
Schedule of debt issuance costs	Deferred debt issuance costs related to our lines of credit included in other long-term assets are as follows (in thousands): December 31, 2017 2018 Debt issuance costs, gross $ 695 $ 334 Less accumulated amortization (366 ) (234 ) Debt issuance costs, net $ 329 $ 100 Deferred debt issuance costs related to our term loans included in debt are as follows (in thousands): December 31, 2017 2018 Debt issuance costs, gross $ 572 $ 30 Less accumulated amortization (246 ) (10 ) Debt issuance costs, net $ 326 $ 20
Schedule of future amortization of debt issuance costs	Future amortization of debt issuance costs is as follows (in thousands): Years Ending December 31, Amortization 2019 $ 89 2020 31 Total $ 120
Schedule of deferred costs	Year Ended December 31, 2016 2017 2018 Beginning balance $ 1,213 $ — $ 3,144 Deferred costs 715 3,144 1,135 Recognized against offering proceeds — — (4,279 ) Write-off of costs related to terminated equity offering $ (1,928 ) $ — $ — Ending balance $ — $ 3,144 $ —
Schedule of restructuring costs	The following table summarizes the allocation of expenses related to the reduction in force on the consolidated statements of operations (in thousands): Year Ended December 31, 2016 Delivery costs $ 93 Sales and marketing 396 Research and development 553 General and administration 249 Total reduction in force costs $ 1,291

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of property and equipment	Depreciation of property and equipment is determined using the straight-line method over the estimated useful lives of the applicable assets, which are as follows: Computer equipment: 2–3 years Furniture and fixtures: 5 years Leasehold improvements: Lesser of estimated useful life or life of the lease Significant components of property and equipment are as follows (in thousands): December 31, 2017 2018 Computer equipment $ 10,827 $ 16,284 Leasehold improvements 5,399 5,573 Furniture and fixtures 824 913 Construction in progress — 65 Property and equipment, gross 17,050 22,835 Less accumulated depreciation (9,731 ) (12,605 ) Property and equipment, net $ 7,319 $ 10,230
Schedule of capital leased assets	Assets acquired under capital leases, included within computer equipment, are as follows (in thousands): December 31, 2017 2018 Capital lease assets, gross $ 1,096 $ 1,096 Less accumulated depreciation (1,022 ) (1,047 ) Capital lease assets, net $ 74 $ 49

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of long-term debt instruments	Our debt consists of the following (in thousands): December 31, 2017 2018 Lines of credit $ 25,081 $ 26,677 Term loans (1) 31,830 19,980 Capital leases 101 57 Total debt 57,012 46,714 Less current portion of long-term debt (44 ) (21 ) Long-term debt, net of current portion $ 56,968 $ 46,693 (1) Net of unamortized discount and debt issuance costs of $1,058 and $20 as of December 31, 2017 and 2018 , respectively.
Schedule of maturities of debt and capital lease	Aggregate future payments of principal and interest due upon maturity are as follows (in thousands): Years Ending December 31, Debt Capital leases Total debt 2019 $ — $ 20 $ 20 2020 46,677 24 46,701 2021 — 13 13 Total principal payments 46,677 57 46,734 Less unamortized debt issuance costs (20 ) — (20 ) Total debt $ 46,657 $ 57 $ 46,714

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Allocation of recognized period costs	The following table summarizes the allocation of stock-based compensation on the consolidated statements of operations (in thousands): Year Ended December 31, 2016 2017 2018 Delivery costs $ 96 $ 202 $ 633 Sales and marketing expense 1,153 1,894 9,358 Research and development expense 574 951 4,087 General and administration expense 1,624 2,100 12,712 Total stock-based compensation expense $ 3,447 $ 5,147 $ 26,790
Summary of common stock option activity	A summary of common stock option activity is as follows (in thousands, except per share amounts): Shares Weighted-Average Exercise Price Per Share Options Outstanding - December 31, 2015 1,676 $ 11.04 Granted 1,330 18.08 Exercised (44 ) 6.00 Forfeited (685 ) 12.50 Cancelled (140 ) 11.82 Options Outstanding - December 31, 2016 2,137 15.00 Granted 799 23.78 Exercised (47 ) 4.83 Forfeited (159 ) 18.24 Cancelled (216 ) 7.54 Options Outstanding - December 31, 2017 2,514 18.42 Granted 29 24.24 Exercised (357 ) 6.25 Forfeited (197 ) 24.10 Cancelled (215 ) 16.60 Options Outstanding - December 31, 2018 1,774 $ 20.55
Summary of RSU activity	A summary of restricted stock unit activity is as follows (in thousands, except per share amounts): Shares Weighted-Average Grant Date Fair Value Per Share Restricted Stock Units Outstanding - December 31, 2017 — $ — Granted 1,309 20.58 Vested (850 ) 21.93 Forfeited (78 ) 17.97 Restricted Stock Units Outstanding - December 31, 2018 381 $ 18.11

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of domestic and foreign components of income (loss) before income taxes	Domestic and foreign components of loss before income taxes are as follows (in thousands): Year Ended December 31, 2016 2017 2018 Domestic $ (73,167 ) $ (16,711 ) $ (48,897 ) Foreign (2,529 ) (2,930 ) (4,145 ) Loss before income taxes $ (75,696 ) $ (19,641 ) $ (53,042 )
Schedule of components of income tax (expense) benefit	The significant components of income tax (expense) benefit are as follows (in thousands): Year Ended December 31, 2016 2017 2018 Current: Federal $ — $ — $ — State — — — Foreign — — — Total current — — — Deferred: Federal 22,449 (28,331 ) 6,896 State 1,796 2,345 1,264 Foreign 864 85 916 Change in uncertain tax positions (117 ) (120 ) (105 ) Change in valuation allowance (24,992 ) 26,021 (8,971 ) Total deferred — — — Income tax benefit $ — $ — $ —
Schedule of effective tax rate	The following table summarizes the significant differences between the U.S. federal statutory tax rate and our effective tax rate: Year Ended December 31, 2016 2017 2018 Tax benefit at federal statutory rate 34.00 % 34.00 % 21.00 % State income taxes, net of federal benefit 1.36 % 1.82 % 1.91 % Change in federal and state statutory rate — % (156.32 )% 0.03 % Foreign rate differential (0.80 )% (1.04 )% (0.06 )% Other adjustments (1.54 )% (10.93 )% (5.97 )% Valuation allowance (33.02 )% 132.47 % (16.91 )% Income tax benefit — % — % — %
Schedule of deferred income taxes	The significant components of deferred income taxes are as follows (in thousands): December 31, 2017 2018 Net operating loss carry-forwards $ 53,182 $ 60,718 Allowance for doubtful accounts 18 26 Depreciation and amortization (485 ) (856 ) Stock-based compensation 1,330 1,968 Deferred costs 1,042 1,334 IRC Section 163(j) interest expense limitation — 737 Other tax credit carry-forward 2,720 3,071 Other temporary differences 842 465 Valuation allowance (58,649 ) (67,463 ) Net long-term deferred tax liability $ — $ —
Summary of changes in valuation allowance	The following table presents changes in our valuation allowance (in thousands): Year Ended December 31, 2016 2017 2018 Beginning balance $ (59,789 ) $ (84,483 ) $ (58,649 ) Allowance for domestic and foreign net operating loss carry-forwards (24,791 ) (6,509 ) (9,863 ) Rate change on domestic net operating loss carry-forwards (15 ) 30,705 (17 ) Change in foreign currency 298 (187 ) 157 Other changes (186 ) 1,825 909 Ending balance $ (84,483 ) $ (58,649 ) $ (67,463 )
Schedule of unrecognized tax benefits activity	The following table summarizes the activity related to our gross unrecognized tax benefits that would affect our effective tax rate, if recognized (in thousands): Year Ended December 31, 2016 2017 2018 Beginning balance $ 441 $ 558 $ 678 Increase related to current year tax position 117 120 105 Ending balance $ 558 $ 678 $ 783

REDEEMABLE CONVERTIBLE PREFER_2

REDEEMABLE CONVERTIBLE PREFERRED STOCK (Tables)	12 Months Ended
	Dec. 31, 2018
Temporary Equity Disclosure [Abstract]
Summary of the change in carrying amount of the outstanding redeemable convertible preferred stock	A summary of the change in carrying amount of the outstanding redeemable convertible preferred stock is as follows (in thousands): Series G’ Stock Series G Stock Shares Amount Shares Amount Balance — December 31, 2016 — $ — — $ — Issuance of Series G and Series G’ Stock 1,296 44,672 346 4,488 Beneficial conversion feature of Series G stock — — — (4,488 ) Deemed dividend related to beneficial conversion feature 4,488 Accretion of redeemable convertible preferred stock — — — 622 Balance — December 31, 2017 1,296 44,672 346 5,110 Accretion of redeemable convertible preferred stock — — — 108 Conversion of preferred stock to common stock (1,296 ) (44,672 ) (346 ) (5,218 ) Balance — December 31, 2018 — $ — — $ — Series F/F-R Stock Series E/E-R Stock Series D/D-R Stock Shares Amount Shares Amount Shares Amount Balance — December 31, 2015 1,199 $ 57,204 1,193 $ 44,922 1,396 $ 32,509 Accretion of redeemable convertible preferred stock — 754 — 19 — 133 Conversion of preferred stock to common stock — — (398 ) (14,978 ) — — Balance — December 31, 2016 1,199 $ 57,958 795 $ 29,963 1,396 $ 32,642 Accretion of redeemable convertible preferred stock — 491 — 9 — 86 Balance — December 31, 2017 1,199 $ 58,449 795 $ 29,972 1,396 $ 32,728 Accretion of redeemable convertible preferred stock — 38 — 1 — 7 Conversion of preferred stock to common stock (1,199 ) (58,487 ) (795 ) (29,973 ) (1,396 ) (32,735 ) Balance — December 31, 2018 — $ — — $ — — $ — Series C/C-R Stock Series B/B-R Stock Series A/A-R Stock Shares Amount Shares Amount Shares Amount Balance — December 31, 2015 1,508 $ 18,254 2,249 $ 5,287 1,869 $ 1,885 Accretion of redeemable convertible preferred stock — 69 — 4 — 3 Conversion of preferred stock to common stock — — (2 ) (5 ) (12 ) (38 ) Balance — December 31, 2016 1,508 $ 18,323 2,247 $ 5,286 1,857 $ 1,850 Accretion of redeemable convertible preferred stock — 43 — 2 — 2 Balance — December 31, 2017 1,508 $ 18,366 2,247 $ 5,288 1,857 $ 1,852 Accretion of redeemable convertible preferred stock — 3 — — — — Conversion of preferred stock to common stock (1,508 ) (18,369 ) (2,247 ) (5,288 ) (1,857 ) (1,852 ) Balance — December 31, 2018 — $ — — $ — — $ —

COMMON STOCK WARRANTS (Tables)

COMMON STOCK WARRANTS (Tables)	12 Months Ended
	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Summary of common stock warrant activity	A summary of common stock warrant activity, exclusive of the common stock warrants issued in connection with our Series G financing is as follows (in thousands, except per share amounts): Shares Weighted-average exercise price per share Warrants Outstanding - December 31, 2015 448 $ 5.28 Granted 97 20.00 Redeemable convertible preferred stock warrants converted to common stock warrants 38 1.92 Warrants Outstanding - December 31, 2016 583 7.52 Granted 17 27.68 Warrants Outstanding - December 31, 2017 600 8.11 Granted (1) 644 23.64 Exercised (349 ) 4.69 Redeemable convertible preferred stock warrants converted to common stock warrants 110 12.16 Forfeited/canceled (138 ) 5.85 Warrants Outstanding - December 31, 2018 867 $ 21.89 (1) Performance-based warrants to purchase 644,365 shares of our Series E Stock, which were converted to common stock warrants, vested upon the completion of our IPO in February 2018. These warrants are not included within this table in periods prior to their vesting. A summary of our preferred stock warrants is as follows (in thousands, except per share amounts): December 31, Preferred Series Grant date Expiration date Exercise price 2016 2017 2018 Series B-R 2/26/2010 2/25/2020 $ 2.36 59 59 — Series D-R 9/21/2012 9/20/2022 $ 23.64 38 38 — Series D-R 9/21/2012 9/20/2022 $ 23.64 13 13 — Total preferred stock warrants 110 110 —

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of financial assets and liabilities measured at fair value on a recurring basis	Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The following table summarizes our liabilities measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Liabilities: Preferred stock warrants (1) $ — $ — $ 2,285 $ 2,285 Common stock warrants (1) — — 7,945 7,945 Total liabilities $ — $ — $ 10,230 $ 10,230 (1) Warrant liabilities were zero as of December 31, 2018 .
Schedule of reconciliation of the redeemable convertible preferred stock warrant liability	Our redeemable convertible preferred stock warrants, common stock warrants issued in connection with the Series G Stock financing and our convertible promissory notes are measured and recorded at fair value on a recurring basis using Level 3 inputs. The table below provides a roll forward of the changes in fair value of Level 3 financial instruments (in thousands): Preferred Common Convertible Balance at December 31, 2015 $ 2,942 — $ — Fair value of convertible promissory notes at issuance — — 66,391 Accrued interest on convertible promissory notes — — 2,876 Conversion of preferred stock warrants to common stock warrants (777 ) — — Changes in fair value 32 — 3,065 Balance at December 31, 2016 $ 2,197 $ — $ 72,332 Preferred Common Convertible Balance at December 31, 2016 $ 2,197 $ — $ 72,332 Conversion of convertible promissory notes to Series G’ preferred stock — — (44,672 ) Conversion of convertible promissory notes to common stock — — (24,392 ) Accrued interest on convertible promissory notes — — 1,701 Issuance of common stock warrants — 7,452 — Changes in fair value 88 493 (4,969 ) Balance at December 31, 2017 $ 2,285 $ 7,945 $ — Preferred Stock Warrants Common Stock Warrants Convertible Promissory Notes Balance at December 31, 2017 $ 2,285 $ 7,945 $ — Conversion of preferred stock warrants to common stock warrants (1,736 ) — — Changes in fair value (549 ) 7,309 — Exercise of common stock warrants — (15,254 ) — Balance at December 31, 2018 $ — $ — $ —
Fair value inputs	The following table summarizes key assumptions used in the PWERM for estimating the fair value of our redeemable convertible preferred stock warrant liability: December 31, 2016 2017 Cost of debt applicable to convertible promissory notes 12% to 17% —% Cost of equity applicable to convertible promissory notes 24% to 26% —% Weighted-average cost of capital applicable to preferred stock warrants 23% 21% Discount for lack of marketability 8% to 12% 7% to 13% Volatility 54% 55% Risk-free interest rate 0.7% to 1.2% 1.2% to 1.4% We determined the fair value of these common warrants on the date of IPO using the Black-Scholes option pricing model, which is affected by the fair value of our common stock as well as the following significant inputs: February 8, 2018 Weighted-average grant date fair value $3.91 Significant inputs: Value of common stock $13.00 Expected term 5.3 years Volatility 50% Risk-free interest rate 2.0% Dividend yield —% Common stock Common stock Weighted-average grant date fair value $10.44 $19.04 Significant inputs: Value of common stock $17.92 $30.08 Expected term 10 years 10 years Volatility 51% 50% Risk-free interest rate 1.2% 2.2% Dividend yield —% —%
Summary of our preferred stock warrants	A summary of common stock warrant activity, exclusive of the common stock warrants issued in connection with our Series G financing is as follows (in thousands, except per share amounts): Shares Weighted-average exercise price per share Warrants Outstanding - December 31, 2015 448 $ 5.28 Granted 97 20.00 Redeemable convertible preferred stock warrants converted to common stock warrants 38 1.92 Warrants Outstanding - December 31, 2016 583 7.52 Granted 17 27.68 Warrants Outstanding - December 31, 2017 600 8.11 Granted (1) 644 23.64 Exercised (349 ) 4.69 Redeemable convertible preferred stock warrants converted to common stock warrants 110 12.16 Forfeited/canceled (138 ) 5.85 Warrants Outstanding - December 31, 2018 867 $ 21.89 (1) Performance-based warrants to purchase 644,365 shares of our Series E Stock, which were converted to common stock warrants, vested upon the completion of our IPO in February 2018. These warrants are not included within this table in periods prior to their vesting. A summary of our preferred stock warrants is as follows (in thousands, except per share amounts): December 31, Preferred Series Grant date Expiration date Exercise price 2016 2017 2018 Series B-R 2/26/2010 2/25/2020 $ 2.36 59 59 — Series D-R 9/21/2012 9/20/2022 $ 23.64 38 38 — Series D-R 9/21/2012 9/20/2022 $ 23.64 13 13 — Total preferred stock warrants 110 110 —

RELATED PARTIES (Tables)

RELATED PARTIES (Tables)	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Schedule of related party transactions	The following table summarizes purchases of our convertible promissory notes by our directors, executive officers and holders of more than 5% of any class of our capital stock as of the date of such transaction (in thousands): Related Party Principal amount of convertible notes Aeroplan Holdings Europe Sàrl(1) $ 3,987 Entities affiliated with Polaris Venture Partners(2) 5,321 Canaan VIII L.P.(3) 6,514 Entities affiliated with Discovery Capital(4) 2,663 Scott D. Grimes 650 Lynne M. Laube 350 (1) Aeroplan Holdings Europe Sàrl is an affiliate of Aimia Inc. David L. Adams, a member of our board of directors, was the Executive Vice President and Chief Financial Officer of Aimia Inc. at the time of the issuance. (2) Consists of convertible promissory notes in an aggregate principal amount of $5,134,443.03 purchased by Polaris Venture Partners V, L.P. ("PVP V") convertible promissory notes in an aggregate principal amount of $100,069.82 purchased by Polaris Venture Partners Entrepreneurs’ Fund V, L.L. ("PVP EF V") convertible promissory notes in an aggregate principal amount of $35,170.61 purchased by Polaris Venture Partners Founders’ Fund V, L.P. ("PVP FF V") and convertible promissory notes in an aggregate principal amount of $51,344.45 purchased by Polaris Venture Partners Special Founders’ Fund V, L.P. ("PVP SFF V") Polaris Venture Management Co. V, L.L.C. (“PVM V”) is the general partner of each PVP V, PVP EF V, PVP FF V, and PVP SFF V (collectively, the “Polaris Funds”). PVM V may be deemed to have sole power to vote and dispose of the shares held by each of the Polaris Funds. Each of Jonathan Flint and Terrance McGuire (collectively, the “Managing Members”) are the managing members of PVM V and may be deemed to share voting and dispositive power with respect to the shares held by the Polaris Funds. Bryce Youngren, a member of our board of directors, has a membership interest in PVM V, and may be deemed to share voting and dispositive powers with respect to the shares held by the Polaris Funds by virtue of his relationship to PVM V. Each of PVM V, the Managing Members and Mr. Youngren disclaim beneficial ownership of all of the shares owned by the Polaris Funds, and this report shall not be deemed an admission that any of PVM V, the Managing Members or Mr. Youngren is the beneficial owner of the shares owned by the Polaris Funds for purposes of Section 16 or for any other purpose, except to the extent of their respective and proportionate pecuniary interests therein. (3) John V. Balen, a member of our board of directors, is a managing member of Canaan Partners VIII LLC, the general partner of Canaan VIII L.P. Mr. Balen does not have voting or investment power over any shares held directly by Canaan VIII L.P. The following table summarizes the participation in the foregoing transactions by our directors, executive officers and holders of more than 5% of any class of our capital stock as of the date of such transactions (in thousands): Related Party Shares of Series G Preferred Stock Shares of Series G’ Preferred Stock Shares of Common Stock Warrants to Purchase Common Stock Entities affiliated with Aimia, Inc. (1) — 382 801 — Entities affiliated with Polaris Venture Partners (2) 29 212 — 66 Canaan VIII L.P. (3) 54 260 — 123 Entities affiliated with Discovery Capital (4) — 106 — — Scott D. Grimes — 26 — — Lynne M. Laube — 14 — — Entities affiliated with Mark A. Johnson (5) 35 15 — 80 John Klinck 6 — — 13 David Adams 3 — — 7 (1) Consists of 159,207 shares of Series G’ redeemable convertible preferred stock issued to Aeroplan Holdings Europe Sàrl, 223,020 shares of Series G’ redeemable convertible preferred stock issued to Aimia EMEA Limited and 801,329 shares of common stock issued to Aimia EMEA Limited. (2) Consists of 27,988 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners V, L.P. (“PVP V”), 205,020 shares of Series G’ redeemable convertible preferred stock issued to PVP V, 64,038 warrants to purchase common stock issued to PVP V, 545 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners Entrepreneurs’ Fund V, L.L. (“PVP EF V”), 3,995 shares of Series G’ redeemable convertible preferred stock issued to PVP EF V, 1,247 warrants to purchase common stock issued to PVP EF V, 191 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners Founders’ Fund V, L.P. (“PVP FF V”), 1,404 shares of Series G’ redeemable convertible preferred stock issued to PVP FF V, 438 warrants to purchase common stock issued to PVP FF V, 280 shares of Series G redeemable convertible preferred stock purchased by Polaris Venture Partners Special Founders’ Fund V, L.P. (“PVP SFF V”), 2,050 shares of Series G’ redeemable convertible preferred stock issued to PVP SFF V and 641 warrants to purchase common stock issued to PVP SFF V. Polaris Venture Management Co. V, L.L.C. is a general partner of each of PVP V, PVP EF V, PVP FF V and PVP SFF V and may be deemed to have the sole voting and dispositive power over the shares held by PVP V, PVP EF V, PVP FF V and PVP SFF V. Bryce Youngren, a member of our board of directors, is a Managing Partner of Polaris Partners and may be deemed to share voting and dispositive power over the shares held by PVP V, PVP EF V, PVP FF V and PVP SFF V. (3) John V. Balen, a member of our board of directors, is a managing member of Canaan Partners VIII LLC, the general partner of Canaan VIII L.P. Mr. Balen does not have voting or investment power over any shares held directly by Canaan VIII L.P. (4) Consists of 95,272 shares of Series G’ redeemable convertible preferred stock issued to Discovery Opportunity Master Fund, Ltd. and 11,072 shares of Series G’ redeemable convertible preferred stock issued to Discovery Global Focus Master Fund, Ltd. (5) Consists of 15,045 shares of Series G’ redeemable convertible preferred stock issued to TTP Fund II, L.P., 29,005 shares of Series G redeemable convertible preferred stock purchased by TTV Ivy Holdings, LLC, 66,365 warrants to purchase common stock issued to TTV Ivy Holdings, LLC, 5,801 shares of Series G redeemable convertible preferred stock purchased by Mr. Johnson, and 13,273 warrants to purchase common stock issued to Mr. Johnson. TTV Capital is a provider of management services to TTP GP II, LLC, which is a general partner of TTP Fund II, L.P. TTV Capital is the manager of TTV Ivy Holdings Manager, LLC, which is the general partner of TTV Ivy Holdings, LLC. Mark A. Johnson, a member of our board of directors, is a member of each of TTP GP II, LLC and TTV Ivy Holdings Managers, LLC and holds the title of partner of TTV Capital, and may be deemed to share voting and dispositive power over the shares held by TTP Fund II L.P. and TTV Ivy Holdings, LLC.

VARIABLE INTEREST ENTITY (Table

VARIABLE INTEREST ENTITY (Tables)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Operating expense reimbursements and allocation of revenue less FI Share and third-party costs	Operating expense reimbursements and allocation of revenue less FI Share and third-party costs (recorded in FI Share and other third-party costs), are as follows (in thousands): Year Ended December 31, 2016 Operating expense reimbursements: Delivery costs $ 24 Sales and marketing expense 597 General and administrative expense 129 Allocation of revenue less FI Share and other third-party costs $ 1,223

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Deferred FI implementation costs	The following table presents changes in deferred FI implementation costs (in thousands): December 31, 2016 2017 2018 Beginning balance $ 1,936 $ 8,451 $ 13,625 Deferred costs 8,205 10,900 9,250 Recoveries through FI Share — (4,100 ) (5,380 ) Amortization (876 ) (1,626 ) (1,618 ) Impairment (814 ) — — Ending balance $ 8,451 $ 13,625 $ 15,877
Schedule of Payments to FI Partners	Payments to FI partners for enhancements not yet placed in service totaled $5.3 million as of December 31, 2018 . Future amortization, based on the amounts earned as of December 31, 2018 , exclusive of amounts expected to be recovered, is as follows (in thousands): Years Ending December 31, Amortization 2019 $ 3,744 2020 3,628 2021 3,245 Total $ 10,617
Future Operating Lease Payments	As of December 31, 2018 , future minimum lease payments under non-cancellable operating leases are as follows (in thousands): Years Ending December 31, Minimum Lease Payments 2019 $ 2,706 2020 2,089 2021 1,654 2022 1,703 2023 1,755 Thereafter 2,418 Total $ 12,325

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of antidilutive securities	The following securities have been excluded from the calculation of diluted weighted-average common shares outstanding because the effect is anti-dilutive (in thousands): December 31, 2016 2017 2018 Redeemable convertible preferred stock: Series A-R 1,857 1,857 — Series B-R 2,247 2,247 — Series C-R 1,508 1,508 — Series D-R 1,396 1,396 — Series E-R 795 795 — Series F-R 1,199 1,199 — Series G — 346 — Series G’ — 1,296 — Common stock options 2,137 2,514 1,774 Common stock warrants 1,227 1,245 867 Common stock warrants issuable pursuant to Series G Stock financing — 547 — Redeemable convertible preferred stock warrants 110 110 — Restricted stock units — — 381 Restricted securities units 53 37 — Convertible promissory notes 2,734 — — Common stock issuable pursuant to the ESPP — — 36

SEGMENTS (Tables)

SEGMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of segment reporting information	The following table provides information regarding our reportable segments (in thousands): Year Ended December 31, 2016 2017 2018 Cardlytics Direct: Adjusted contribution (2)(3) $ 41,374 $ 55,184 $ 69,364 Plus: FI Share and other third-party costs (1) 56,415 67,207 79,959 Revenue $ 97,789 $ 122,391 $ 149,323 Other Platform Solutions: Adjusted contribution $ 6,852 $ 3,560 $ 86 Plus: FI Share and other third-party costs (1) 8,180 4,414 1,275 Revenue $ 15,032 $ 7,974 $ 1,361 Total: Adjusted contribution (2)(3) $ 48,226 $ 58,744 $ 69,450 Plus: FI Share and other third-party costs (1) 64,595 71,621 81,234 Revenue $ 112,821 $ 130,365 $ 150,684 (1) FI Share and other third party costs presented above excludes a non-cash equity expense and amortization and impairment of deferred FI implementation costs, which are detailed below in our reconciliation of GAAP loss before income taxes to non-GAAP adjusted contribution. (2) Adjusted contribution includes the impact of an accrued expense totaling $2.6 million during 2016 related to shortfall in meeting a minimum FI Share commitment. There was no corresponding accrued expense during 2017 and 2018. (3) Adjusted contribution includes the impact of a $0.8 million gain during 2018 related to the renewal of our agreement with Lloyds, which contains certain amendments that are retroactively applied as of January 1, 2018. The following table presents a reconciliation of loss before income taxes presented in accordance with GAAP to adjusted contribution (in thousands): Year Ended December 31, 2016 2017 2018 Adjusted contribution $ 48,226 $ 58,744 $ 69,450 Minus: Non-cash equity expense included in FI Share (1) — — 2,519 Amortization and impairment of deferred FI implementation costs (1) 1,690 1,626 1,618 Delivery costs 6,127 7,012 10,632 Sales and marketing expense 31,261 31,927 41,878 Research and development expense 13,902 12,150 16,210 General and administration expense 21,355 20,100 34,228 Depreciation and amortization expense 4,219 3,028 3,282 Termination of U.K. agreement expense 25,904 — — Total other expense 19,464 2,542 12,125 Loss before income taxes $ (75,696 ) $ (19,641 ) $ (53,042 ) (1) Non-cash equity expense included in FI Share and amortization and impairment of deferred FI implementation costs are excluded from FI Share and other third party costs, which is shown above in our reconciliation of GAAP revenue to non-GAAP adjusted contribution.
Schedule of revenue by geographic areas	The following tables provides geographical information (in thousands): Year Ended December 31, 2016 2017 2018 Revenue: United States $ 100,590 $ 113,509 $ 131,563 United Kingdom 12,231 16,856 19,121 Total $ 112,821 $ 130,365 $ 150,684 December 31, 2017 2018 Property and equipment: United States $ 6,813 $ 9,794 United Kingdom 506 436 Total $ 7,319 $ 10,230

NATURE OF OPERATIONS (Details)

NATURE OF OPERATIONS (Details)	Feb. 14, 2018USD ($)shares	Feb. 14, 2018USD ($)shares	Feb. 13, 2018USD ($)$ / sharesshares	Jan. 26, 2018USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)	Sep. 30, 2018$ / sharesshares	May 31, 2017shares	Feb. 28, 2017shares	May 04, 2012
Debt Instrument [Line Items]
Proceeds from issuance of common stock, threshold | $				$ 70,000,000
Common stock, shares authorized (in shares) | shares				100,000,000	100,000,000	83,000,000		100,000,000	83,000,000
Par value (in usd per share) | $ / shares				$ 0.0001	$ 0.0001	$ 0.0001		$ 0.0001
Preferred stock, par or stated value per share (in usd per share) | $ / shares								$ 0.0001
Shares authorized (in shares) | shares				25,000,000					96,131,002	82,683,212
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares				$ 0.0001
Sale of stock, number of shares issued in transaction (in shares) | shares	421,355	5,821,355
Proceeds from IPO | $	$ 5,500,000	$ 75,700,000
Proceeds from IPO, net | $		66,100,000
Sale of stock, discounts and commissions | $		5,300,000
Issuance costs | $		$ 4,300,000			$ 4,279,000	$ 0	$ 0
Stock split, conversion ratio					0.25
Preferred stock, shares authorized (in shares) | shares								10,000,000
IPO
Debt Instrument [Line Items]
Sale of stock, number of shares issued in transaction (in shares) | shares			5,400,000
Sale of stock, price per share (in usd per share) | $ / shares			$ 13
Proceeds from IPO | $			$ 70,200,000
Over-Allotment Option
Debt Instrument [Line Items]
Sale of stock, number of shares issued in transaction (in shares) | shares	810,000
Cardlytics UK
Debt Instrument [Line Items]
Collaboration Agreement, income (loss), percentage											50.00%

SIGNIFICANT ACCOUNTING POLICI_4

SIGNIFICANT ACCOUNTING POLICIES - Foreign Currency (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Foreign Currency Transaction (Gain) Loss	$ 1.2	$ (1.3)	$ 1.9

SIGNIFICANT ACCOUNTING POLICI_5

SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016
Concentration Risk [Line Items]
Number of reportable segments | segment	2
Capitalized software development costs, net | $	$ 1,625	$ 433
Product Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk	68.00%	66.00%	67.00%

SIGNIFICANT ACCOUNTING POLICI_6

SIGNIFICANT ACCOUNTING POLICIES - Consumer Incentives (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Consumer incentives, expense	$ 68.3	$ 61.2	$ 57

SIGNIFICANT ACCOUNTING POLICI_7

SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable (Details) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ 105	$ 653	$ 746
Bad debt expense	130	73	1,100
Write-offs, net of recoveries	(66)	(621)	(1,193)
Ending balance	169	105	653
Unbilled receivables	$ 400	$ 100	$ 500

SIGNIFICANT ACCOUNTING POLICI_8

SIGNIFICANT ACCOUNTING POLICIES - Concentrations of Risk (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Financial institutions agreement, notice period		90 days
Debt issuance costs, net	$ 20	$ 20	$ 1,058
Product Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk		68.00%	66.00%	67.00%
Minimum
Concentration Risk [Line Items]
Financial institutions agreement, term		3 years
Maximum
Concentration Risk [Line Items]
Financial institutions agreement, term		5 years
Largest FI Partner | Product Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk	17.00%
United States | Largest FI Partner | Product Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk	55.00%	64.00%	63.00%	64.00%
United Kingdom | Largest FI Partner | Product Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk	8.00%	9.00%	12.00%	10.00%

SIGNIFICANT ACCOUNTING POLICI_9

SIGNIFICANT ACCOUNTING POLICIES - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Interest-bearing deposits, interest rate	1.05%
Restricted cash deposits, interest rate	1.35%
Cash and cash equivalents	$ 39,623	$ 21,262	$ 39,623	$ 22,838
Restricted cash		0	20,247	130
Cash, cash equivalents and restricted cash	$ 59,870	$ 21,262	$ 59,870	$ 22,968	$ 27,609

SIGNIFICANT ACCOUNTING POLIC_10

SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2018
Computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	2 years
Computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Useful life	5 years

SIGNIFICANT ACCOUNTING POLIC_11

SIGNIFICANT ACCOUNTING POLICIES - Intangible Assets (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)patent	Dec. 31, 2013patent	Dec. 31, 2017USD ($)
Accounting Policies [Abstract]
Number of patents | patent	1	3
Finite-lived intangible assets, not yet capitalized	$ 200		$ 400
Estimated amortization expense, 2019	100
Estimated amortization expense, 2020	100
Estimated amortization expense, 2021	100
Estimated amortization expense, 2022	100
Estimated amortization expense, 2023	100
Deferred patent costs, gross	417		563
Less accumulated amortization	(47)		(35)
Deferred patent costs, net	$ 370		$ 528

SIGNIFICANT ACCOUNTING POLIC_12

SIGNIFICANT ACCOUNTING POLICIES - Capitalized Software (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Write off, capitalized computer software	$ 1,200
Capitalized software development costs, gross		$ 2,826	$ 1,487
Less accumulated amortization		(1,201)	(1,054)
Capitalized software development costs, net		$ 1,625	$ 433

SIGNIFICANT ACCOUNTING POLIC_13

SIGNIFICANT ACCOUNTING POLICIES - Impairment of Long-Lived Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Deferred FI cost, impairment loss	$ 0	$ 0	$ (814,000)

SIGNIFICANT ACCOUNTING POLIC_14

SIGNIFICANT ACCOUNTING POLICIES - Debt Issuance Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 21, 2018
Debt Instrument [Line Items]
Loss on extinguishment of debt	$ 900
Amortization of financing costs charged to interest expense	282	$ 560	$ 297
Debt issuance costs			$ 700
Debt issuance costs, net	20	1,058
2,019	89
2,020	31
Total	120
Lines of credit
Debt Instrument [Line Items]
Debt issuance costs, gross	334	695		$ 100
Less accumulated amortization	(234)	(366)
Debt issuance costs, net	100	329
Term loans
Debt Instrument [Line Items]
Debt issuance costs, gross	30	572
Less accumulated amortization	(10)	(246)
Debt issuance costs, net	$ 20	$ 326
2016 Line of Credit and 2016 Term Loan
Debt Instrument [Line Items]
Debt issuance costs, net				$ 100

SIGNIFICANT ACCOUNTING POLIC_15

SIGNIFICANT ACCOUNTING POLICIES - Deferred Offering Costs (Details) - USD ($) $ in Thousands	Feb. 14, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Financial Institution Costs [Roll Forward]
Beginning balance		$ 3,144	$ 0	$ 1,213
Deferred costs		1,135	3,144	715
Recognized against offering proceeds	$ (4,300)	(4,279)	0	0
Write-off of costs related to terminated equity offering		0	0	(1,928)
Ending balance		$ 0	$ 3,144	$ 0

SIGNIFICANT ACCOUNTING POLIC_16

SIGNIFICANT ACCOUNTING POLICIES - Reduction in Force (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Award vesting period	4 years
Stock-based compensation expense	$ 26,790	$ 5,147	$ 3,447
Severance Costs			1,291
Delivery costs
Restructuring Cost and Reserve [Line Items]
Stock-based compensation expense	633	202	96
Severance Costs			93
Sales and marketing expense
Restructuring Cost and Reserve [Line Items]
Stock-based compensation expense	9,358	1,894	1,153
Severance Costs			396
Research and development expense
Restructuring Cost and Reserve [Line Items]
Stock-based compensation expense	4,087	951	574
Severance Costs			553
General and administration expense
Restructuring Cost and Reserve [Line Items]
Stock-based compensation expense	$ 12,712	$ 2,100	1,624
Severance Costs			$ 249
Reduction In Force
Restructuring Cost and Reserve [Line Items]
Award vesting period			2 years
Stock-based compensation expense			$ 100
Severance Costs			$ 1,300

SIGNIFICANT ACCOUNTING POLIC_17

SIGNIFICANT ACCOUNTING POLICIES - Advertising costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Advertising expense	$ 0.9	$ 0.7	$ 0.9

SIGNIFICANT ACCOUNTING POLIC_18

SIGNIFICANT ACCOUNTING POLICIES - Fair Value of Financial Instruments (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Aug. 31, 2018	May 31, 2017	Dec. 31, 2018	Aug. 08, 2018	May 31, 2013
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)					$ 23.64
Series G Stock
Class of Stock [Line Items]
Exercise of common stock warrants (in shares)	792,434
Conversion of securities to common stock (in shares)	792,434		346,000
Exercise price of warrants (in usd per share)	$ 0.0004			$ 0.0004
Issuance of stock	$ 15.3	$ 11.9

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 22,835	$ 17,050
Less accumulated depreciation	(12,605)	(9,731)
Property, Plant and Equipment, Net	10,230	7,319
Capital lease assets, gross	1,096	1,096
Less accumulated depreciation	(1,047)	(1,022)
Capital lease assets, net	49	74
Depreciation expense	3,000	3,000	$ 3,000
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	16,284	10,827
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,573	5,399
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	913	824
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 65	$ 0

DEBT - Schedule of Debt (Detail

DEBT - Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total debt	$ 46,714	$ 57,012
Less current portion of long-term debt	(21)	(44)
Long-term debt, net of current portion	46,693	56,968
Debt issuance costs, net	20	1,058
Lines of credit
Debt Instrument [Line Items]
Total debt	26,677	25,081
Debt issuance costs, net	100	329
Term loans
Debt Instrument [Line Items]
Total debt	19,980	31,830
Debt issuance costs, net	20	326
Capital leases
Debt Instrument [Line Items]
Total debt	$ 57	$ 101

DEBT - Narrative (Details)

DEBT - Narrative (Details)	1 Months Ended		12 Months Ended
	Nov. 30, 2018USD ($)	Aug. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)shares	Dec. 31, 2018GBP (£)	Dec. 31, 2018USD ($)	May 21, 2018USD ($)	Sep. 30, 2016USD ($)	Jul. 31, 2016USD ($)
Debt Instrument [Line Items]
Accrued interest (less than)				$ 6,200,000			$ 0
Cash paid for interest			$ 9,700,000	900,000	$ 1,600,000
Debt issuance costs, net				1,058,000			$ 20,000
Maximum borrowing capacity, percentage of accounts receivable						85.00%	85.00%
Revenue, threshold			134,500,000
Debt instrument, required cash balance							$ 5,000,000
Repayments of lines of credit			52,581,000	99,000	32,346,000
Loss on extinguishment of debt			900,000
Decrease in fair value of convertible promissory notes			0	1,244,000	786,000
Termination of U.K. agreement expense			0	0	25,904,000
Capital lease obligations				0	100,000		0
2016 Line of Credit and 2016 Term Loan
Debt Instrument [Line Items]
Debt issuance costs, net								$ 100,000
Lines of credit
Debt Instrument [Line Items]
Maximum borrowing capacity							30,000,000
Proceeds from lines of credit			$ 27,400,000
Debt issuance costs, gross				695,000			334,000	$ 100,000
Debt issuance costs, net				329,000			100,000
Debt instrument, interest rate								4.75%
Commitment fee percentage			0.15%
Debt Instrument, success fee			$ 75,000
Revenue threshold, trailing four quarter revenue							200,000,000
Debt instrument, collateral amount							$ 20,000,000
Debt instrument, interest rate increase event of default						3.00%	3.00%
Repayments of lines of credit	$ 100,000	$ 700,000
Line of credit facility, remaining borrowing capacity							$ 3,300,000
Lines of credit | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate			(0.75%)
Lines of credit | Loan Facility, Threshold One
Debt Instrument [Line Items]
Line of credit, deposit threshold							40,000,000
Lines of credit | Loan Facility, Threshold One | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate			(0.75%)
Lines of credit | Loan Facility, Threshold Two | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate			(0.50%)
Lines of credit | Loan Facility, Threshold Three
Debt Instrument [Line Items]
Line of credit, deposit threshold							20,000,000
Lines of credit | 2016 Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity									$ 50,000,000
Loss on extinguishment of debt			$ 100,000
Term loans
Debt Instrument [Line Items]
Debt instrument, face amount								$ 20,000,000
Debt issuance costs, gross				572,000			30,000
Debt issuance costs, net				326,000			$ 20,000
Debt instrument, interest rate						2.75%	2.75%
Term loans | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate			(2.75%)
Term loans | 2016 Term Loan
Debt Instrument [Line Items]
Debt instrument, face amount										$ 24,000,000
Loss on extinguishment of debt			$ 800,000
Convertible Promissory Notes
Debt Instrument [Line Items]
Debt instrument, face amount							$ 50,700,000
Convertible Promissory Notes | Aimia EMEA Notes
Debt Instrument [Line Items]
Debt instrument, face amount					$ 18,000,000
Debt instrument, stated interest rate					10.00%
Convertible debt instrument, equity financing proceeds trigger					$ 10,000,000
Convertible debt instrument, percentage of stock price trigger					80.00%
Convertible debt instrument, shares converted (in shares) | shares					801,329
Decrease in fair value of convertible promissory notes					$ 7,600,000
Termination of U.K. agreement expense					7,900,000
Convertible Promissory Notes | Outstanding Obligation Note
Debt Instrument [Line Items]
Debt instrument, face amount					$ 5,700,000
Debt instrument, stated interest rate					10.00%
Revolving Credit Facility | Lines of credit
Debt Instrument [Line Items]
Maximum borrowing capacity								$ 30,000,000
Working Capital Line of Credit | Lines of credit
Debt Instrument [Line Items]
Maximum borrowing capacity | £						£ 3,000,000
Basis spread on variable rate			5.25%
Maximum | Lines of credit | Loan Facility, Threshold Two
Debt Instrument [Line Items]
Line of credit, deposit threshold							$ 40,000,000
Maximum | Capital leases
Debt Instrument [Line Items]
Debt instrument, interest rate						13.30%	13.30%
Minimum | Lines of credit | Loan Facility, Threshold Two
Debt Instrument [Line Items]
Line of credit, deposit threshold							$ 20,000,000
Minimum | Capital leases
Debt Instrument [Line Items]
Debt instrument, interest rate						0.00%	0.00%
Convertible Promissory Notes
Debt Instrument [Line Items]
Paid-in-king interest				$ 1,700,000	$ 2,900,000

DEBT - Future Payments (Details

DEBT - Future Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt
2,019	$ 0
2,020	46,677
2,021	0
Total principal payments	46,677
Less unamortized debt issuance costs	(20)	$ (1,058)
Total debt	46,657
Capital leases
2,019	20
2,020	24
2,021	13
Total principal payments	57
Total debt
2,019	20
2,020	46,701
2,021	13
Total principal payments	46,734
Less unamortized debt issuance costs	(20)	$ (1,058)
Total debt	$ 46,714

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) $ / shares in Units, user in Millions, $ in Millions

Jan. 01, 2019shares

Feb. 08, 2018$ / sharesshares

Aug. 31, 2018shares

Feb. 28, 2018USD ($)

Mar. 05, 2019USD ($)shares

Dec. 31, 2018USD ($)user$ / sharesshares

Mar. 31, 2018trancheshares

Nov. 15, 2018shares

Dec. 31, 2018USD ($)user$ / sharesshares

Dec. 31, 2017USD ($)$ / sharesshares

Dec. 31, 2016USD ($)$ / shares

Jan. 31, 2018shares

Sep. 30, 2017$ / shares

May 31, 2017shares

May 30, 2017shares

May 15, 2017$ / shares

Feb. 28, 2017$ / shares

Sep. 30, 2016$ / shares

Apr. 30, 2016$ / shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares authorized (in shares)

1,875,000

Number of shares remaining available for issuance (in shares)

61,247

Number of shares authorized, annual increase

5.00%

5.00%

Amounts accrued for capitalized software development costs | $

$ 0.1

Award vesting period

4 years

Expiration period

10 years

Value of stock (in usd per share) | $ / shares

$ 24.24

$ 24.24

$ 26.74

$ 24.48

$ 24.24

$ 30.44

$ 27.68

$ 17.84

$ 19.72

Weighted-average grant date fair value (in usd per share) | $ / shares

$ 3.91

$ 10

$ 12.11

$ 7

Options vested in period, fair value | $

$ 6

$ 4.3

$ 2.9

Compensation not yet recognized | $

$ 6.3

$ 6.3

Compensation cost not yet recognized

2 years

Issuance of ESPP (in shares)

177,238

Restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation cost not yet recognized

2 years 5 months 1 day

Granted (in shares)

1,309,000

Unvested PSU (in shares)

381,000

381,000

0

Forfeited, prior to FI MAU (in shares)

78,000

Vested (in shares)

850,000

Compensation not yet recognized, awards other than options | $

$ 4.5

$ 4.5

Awards granted | $

$ 1

Performance-based restricted share unit

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of tranches | tranche

2

Granted (in shares)

437,500

Unvested PSU (in shares)

875,000

875,000

Vested (in shares)

850,000

Performance-based restricted share unit | Share-based Compensation Award, Tranche One

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award, performance conditions | user

70

70

Forfeited, prior to FI MAU (in shares)

25,000

RSU, performance condition, period

3 years

Performance-based restricted share unit | Share-based Compensation Award, Tranche Two

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award, performance conditions | user

85

85

RSU, performance condition, period

5 years

Stock option expense | $

$ 18.6

Restricted securities units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

RSU, service condition period

6 months

Award period for sale of company or IPO

5 years

Stock option expense | $

$ 0.5

Stock issued during period, RSU (in shares)

37,406

Common stock issuable pursuant to the ESPP

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares authorized, annual increase

1.00%

1.00%

Purchase price of common stock, percent

85.00%

ESPP, number of shares authorized, annual increase (in shares)

500,000

500,000

Minimum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Value of stock (in usd per share) | $ / shares

$ 24.60

$ 17.84

Maximum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Value of stock (in usd per share) | $ / shares

$ 28.16

$ 22.68

2008 Stock Plan

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares authorized (in shares)

4,020,000

3,495,000

3,120,000

2018 Employee Stock Purchase Plan | Common stock issuable pursuant to the ESPP

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares authorized (in shares)

375,000

375,000

Employees and non-employee directors | Restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted (in shares)

434,377

Employees and non-employee directors | Minimum | Restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

1 year

Employees and non-employee directors | Maximum | Restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

4 years

Subsequent Event

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of additional shares authorized (in shares)

1,123,312

Subsequent Event | Restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Granted (in shares)

100,570

Compensation not yet recognized, awards other than options | $

$ 1.8

Subsequent Event | Common stock issuable pursuant to the ESPP

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of additional shares authorized (in shares)

224,662

Subsequent Event | Minimum | Restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

2 years

Subsequent Event | Maximum | Restricted stock units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

4 years

STOCK-BASED COMPENSATION - Allo

STOCK-BASED COMPENSATION - Allocation of Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 26,790	$ 5,147	$ 3,447
Delivery costs
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	633	202	96
Sales and marketing expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	9,358	1,894	1,153
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	4,087	951	574
General and administration expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 12,712	$ 2,100	$ 1,624

STOCK-BASED COMPENSATION - Fair

STOCK-BASED COMPENSATION - Fair Value Assumptions (Details) - $ / shares	Feb. 08, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	May 15, 2017	Feb. 28, 2017	Sep. 30, 2016	Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value (in usd per share)	$ 3.91	$ 10	$ 12.11	$ 7
Significant inputs:
Value of stock (in usd per share)		$ 24.24	$ 26.74	$ 24.48	$ 24.24	$ 30.44	$ 27.68	$ 17.84	$ 19.72
Expected term		7 years	7 years	7 years
Volatility, minimum			50.00%	51.00%
Volatility, maximum			51.00%	56.00%
Volatility		50.00%
Risk-free interest rate, minimum			0.70%	0.50%
Risk-free interest rate, maximum			2.20%	2.10%
Risk-free interest rate		2.70%
Minimum
Significant inputs:
Value of stock (in usd per share)			$ 24.60	$ 17.84
Maximum
Significant inputs:
Value of stock (in usd per share)			$ 28.16	$ 22.68

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Common Stock Option Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Beginning balance (in shares)	2,514	2,137	1,676
Granted (in shares)	29	799	1,330
Exercised (in shares)	(357)	(47)	(44)
Forfeited (in shares)	(197)	(159)	(685)
Canceled (in shares)	(215)	(216)	(140)
Ending balance (in shares)	1,774	2,514	2,137
Weighted-Average Exercise Price
Beginning balance (in usd per share)	$ 18.42	$ 15	$ 11.04
Granted (in usd per share)	24.24	23.78	18.08
Exercised (in usd per share)	6.25	4.83	6
Forfeited (in usd per share)	24.10	18.24	12.50
Canceled (in usd per share)	16.60	7.54	11.82
Ending balance (in usd per share)	$ 20.55	$ 18.42	$ 15

STOCK-BASED COMPENSATION - Su_2

STOCK-BASED COMPENSATION - Summary of RSU Activity (Details) - Restricted stock units shares in Thousands	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Shares
Unvested — Beginning balance (in shares) | shares	0
Granted (in shares) | shares	1,309
Vested (in shares) | shares	(850)
Forfeited (in shares) | shares	(78)
Unvested — Ending balance (in shares) | shares	381
Weighted-Average Grant Date Fair Value
Unvested — Beginning balance (in usd per share) | $ / shares	$ 0
Granted (in usd per share) | $ / shares	20.58
Vested (in usd per share) | $ / shares	21.93
Forfeited (in usd per share) | $ / shares	17.97
Unvested — Ending balance (in usd per share) | $ / shares	$ 18.11

INCOME TAXES - Domestic and For

INCOME TAXES - Domestic and Foreign Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic	$ (48,897)	$ (16,711)	$ (73,167)
Foreign	(4,145)	(2,930)	(2,529)
Loss before income taxes	$ (53,042)	$ (19,641)	$ (75,696)

INCOME TAXES - Components of In

INCOME TAXES - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 0	$ 0	$ 0
State	0	0	0
Foreign	0	0	0
Total current	0	0	0
Deferred:
Federal	6,896	(28,331)	22,449
State	1,264	2,345	1,796
Foreign	916	85	864
Change in uncertain tax positions	(105)	(120)	(117)
Change in valuation allowance	(8,971)	26,021	(24,992)
Total deferred	0	0	0
Income tax benefit	$ 0	$ 0	$ 0

INCOME TAXES - Effective Income

INCOME TAXES - Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Tax benefit at federal statutory rate	21.00%	34.00%	34.00%
State income taxes, net of federal benefit	1.91%	1.82%	1.36%
Change in federal statutory rate	0.03%	(156.32%)	0.00%
Foreign rate differential	(0.06%)	(1.04%)	(0.80%)
Other adjustments	(5.97%)	(10.93%)	(1.54%)
Valuation allowance	(16.91%)	132.47%	(33.02%)
Income tax benefit	0.00%	0.00%	0.00%

INCOME TAXES - Deferred Tax Ass

INCOME TAXES - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net operating loss carry-forwards	$ 60,718	$ 53,182
Allowance for doubtful accounts	26	18
Depreciation and amortization	(856)	(485)
Stock-based compensation	1,968	1,330
Change in fair value of convertible promissory notes	1,334	1,042
IRC Section 163(j) interest expense limitation	737	0
Other tax credit carry-forward	3,071	2,720
Other temporary differences	465	842
Valuation allowance	(67,463)	(58,649)	$ (84,483)	$ (59,789)
Net long-term deferred tax liability	$ 0	$ 0

INCOME TAXES - Change in Valuat

INCOME TAXES - Change in Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Roll Forward]
Beginning balance	$ (58,649)	$ (84,483)	$ (59,789)
Allowance for domestic and foreign net operating loss carry-forwards	(9,863)	(6,509)	(24,791)
Rate change on domestic net operating loss carry-forwards	(17)	30,705	(15)
Change in foreign currency	157	(187)	298
Other changes	909	1,825	(186)
Ending balance	$ (67,463)	$ (58,649)	$ (84,483)

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Tax credits	$ 700	$ 800		$ 600
Cash and cash equivalents	39,623	21,262	$ 39,623	$ 22,838
Cardlytics UK
Operating Loss Carryforwards [Line Items]
Cash and cash equivalents	3,800
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	249,800	220,500
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	90,500	76,300
Foreign
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 13,900	$ 11,400

INCOME TAXES - Unrecognized Tax

INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 678	$ 558	$ 441
Increase related to current year tax position	105	120	117
Ending balance	$ 783	$ 678	$ 558

REDEEMABLE CONVERTIBLE PREFER_3

REDEEMABLE CONVERTIBLE PREFERRED STOCK - Outstanding Stock (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Aug. 31, 2018	May 31, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance				$ 196,437
Issuance of Series G and Series G’ Stock (in shares)					1,296,000
Issuance of Series G and Series G’ Stock				66,101
Conversion of preferred stock to common stock				(196,594)	$ (24,392)	$ (15,021)
Ending balance				$ 0	$ 196,437
Series G’ Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				1,296,000	0
Beginning balance				$ 44,672
Issuance of Series G and Series G’ Stock					$ 44,672
Accretion of redeemable convertible preferred stock				$ 0	0
Conversion of preferred stock to common stock (in shares)				(1,296,000)
Conversion of preferred stock to common stock				$ (44,672)	$ 0
Ending balance (in shares)				0	1,296,000	0
Ending balance				$ 0	$ 44,672
Series G Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				346,000	0
Beginning balance				$ 5,110	$ 0
Issuance of Series G and Series G’ Stock (in shares)		346,334			346,000
Issuance of Series G and Series G’ Stock					$ 4,488
Accretion of redeemable convertible preferred stock				$ 108	622
Conversion of preferred stock to common stock (in shares)	(792,434)			(346,000)
Conversion of preferred stock to common stock				$ (5,218)	(4,488)
Deemed dividend related to beneficial conversion feature			$ 4,500		$ 4,488
Ending balance (in shares)				0	346,000	0
Ending balance				$ 0	$ 5,110	$ 0
Series F/F-R Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				1,199,000	1,199,000	1,199,000
Beginning balance				$ 58,449	$ 57,958	$ 57,204
Accretion of redeemable convertible preferred stock				$ 38	$ 491	$ 754
Conversion of preferred stock to common stock (in shares)				(1,199,000)		0
Conversion of preferred stock to common stock				$ (58,487)		$ 0
Ending balance (in shares)				0	1,199,000	1,199,000
Ending balance				$ 0	$ 58,449	$ 57,958
Series E/E-R Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				795,000	795,000	1,193,000
Beginning balance				$ 29,972	$ 29,963	$ 44,922
Accretion of redeemable convertible preferred stock				$ 1	$ 9	$ 19
Conversion of preferred stock to common stock (in shares)				(795,000)		(398,000)
Conversion of preferred stock to common stock				$ (29,973)		$ (14,978)
Ending balance (in shares)				0	795,000	795,000
Ending balance				$ 0	$ 29,972	$ 29,963
Series D/D-R Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				1,396,000	1,396,000	1,396,000
Beginning balance				$ 32,728	$ 32,642	$ 32,509
Accretion of redeemable convertible preferred stock				$ 7	$ 86	$ 133
Conversion of preferred stock to common stock (in shares)				(1,396,000)		0
Conversion of preferred stock to common stock				$ (32,735)		$ 0
Ending balance (in shares)				0	1,396,000	1,396,000
Ending balance				$ 0	$ 32,728	$ 32,642
Series C/C-R Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				1,508,000	1,508,000	1,508,000
Beginning balance				$ 18,366	$ 18,323	$ 18,254
Accretion of redeemable convertible preferred stock				$ 3	$ 43	$ 69
Conversion of preferred stock to common stock (in shares)				(1,508,000)		0
Conversion of preferred stock to common stock				$ (18,369)		$ 0
Ending balance (in shares)				0	1,508,000	1,508,000
Ending balance				$ 0	$ 18,366	$ 18,323
Series B/B-R Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				2,247,000	2,247,000	2,249,000
Beginning balance				$ 5,288	$ 5,286	$ 5,287
Accretion of redeemable convertible preferred stock				$ 0	$ 2	$ 4
Conversion of preferred stock to common stock (in shares)				(2,247,000)		(2,000)
Conversion of preferred stock to common stock				$ (5,288)		$ (5)
Ending balance (in shares)				0	2,247,000	2,247,000
Ending balance				$ 0	$ 5,288	$ 5,286
Series A/A-R Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance (in shares)				1,857,000	1,857,000	1,869,000
Beginning balance				$ 1,852	$ 1,850	$ 1,885
Accretion of redeemable convertible preferred stock				$ 0	$ 2	$ 3
Conversion of preferred stock to common stock (in shares)				(1,857,000)		(12,000)
Conversion of preferred stock to common stock				$ (1,852)		$ (38)
Ending balance (in shares)				0	1,857,000	1,857,000
Ending balance				$ 0	$ 1,852	$ 1,850

REDEEMABLE CONVERTIBLE PREFER_4

REDEEMABLE CONVERTIBLE PREFERRED STOCK - Financing and Issuances (Details) $ / shares in Units, $ in Thousands	Aug. 08, 2018$ / shares	Aug. 31, 2018USD ($)$ / sharesshares	May 31, 2017USD ($)$ / sharesshares	Sep. 30, 2014USD ($)$ / sharesshares	Jun. 30, 2017USD ($)	Dec. 31, 2018USD ($)installment$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Sep. 30, 2018shares	Jan. 26, 2018$ / sharesshares	Sep. 30, 2017$ / shares	May 15, 2017$ / shares	Feb. 28, 2017$ / sharesshares	Sep. 30, 2016$ / shares	Apr. 30, 2016$ / shares	May 31, 2013$ / shares
Temporary Equity [Line Items]
Shares authorized (in shares)			96,131,002							25,000,000			82,683,212
Shares authorized (in shares)			83,000,000			100,000,000	83,000,000		100,000,000	100,000,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares										$ 0.0001
Issuance costs | $						$ 1,949	$ 2,668	$ 1,674
Conversion of stock, shares converted (in shares)			801,329
Shares issued (in shares)						22,466,000	3,439,000
Exercise price of warrants (in usd per share) | $ / shares																$ 23.64
Proceeds from issuance of preferred stock | $						$ 0	$ 11,940	$ 0
Issuance of Series G and Series G’ Stock (in shares)							1,296,000
Value of stock (in usd per share) | $ / shares						$ 24.24	$ 26.74	$ 24.48			$ 24.24	$ 30.44	$ 27.68	$ 17.84	$ 19.72
Issuance of common stock | $						$ 66,101
Number of quarterly installments, preferred stock | installment						8
Series G’ Stock
Temporary Equity [Line Items]
Shares authorized (in shares)						0	5,339,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares			$ 0.0001			$ 0	$ 0.0001
Conversion of stock, shares converted (in shares)			1,295,746
Conversion Price (in usd per share) | $ / shares			$ 27.58
Shares issued (in usd per share) | $ / shares			2.758
Preferred stock, dividend rate (in usd per share) | $ / shares			2.758
Issuance of common stock | $							$ 44,672
Series G Stock
Temporary Equity [Line Items]
Shares authorized (in shares)						0	1,385,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares			$ 0.0001			$ 0	$ 0.0001
Issuance costs | $			$ 100
Shares issued (in shares)			346,334
Class of warrant, numerator input value (in usd per share) | $ / shares			$ 68.9516
Number of trading days			30 days
Number of days following prospectus	180 days
Exercise price of warrants (in usd per share) | $ / shares	$ 0.0004	$ 0.0004
Exercise of common stock warrants (in shares)		792,434
Issuance of stock | $		$ 15,300	$ 11,900
Proceeds from issuance of preferred stock | $			11,900
Redeemable convertible preferred stock, residual value | $			4,500
Deemed dividend related to beneficial conversion feature | $			$ 6,100
Deemed dividend related to beneficial conversion feature | $					$ 4,500		$ 4,488
Shares issued (in usd per share) | $ / shares			$ 34.4758
Issuance of Series G and Series G’ Stock (in shares)			346,334				346,000
Issuance of common stock | $							$ 4,488
Series F/F-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								1,198,637
Shares authorized (in shares)						0	5,000,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares						$ 0	$ 0.0001
Stock issuance cost, placement fees | $				$ 3,600
Common stock
Temporary Equity [Line Items]
Issuance of Series G and Series G’ Stock (in shares)				199,771
Value of stock (in usd per share) | $ / shares				$ 50.0568
Issuance of common stock | $				$ 10,000
Stock issuance cost, placement fees | $				500
Common stock | General and administration expense
Temporary Equity [Line Items]
Issuance of common stock | $				$ 5,100
Common stock | Fair Value
Temporary Equity [Line Items]
Value of stock (in usd per share) | $ / shares				$ 24.40
Series E/E-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								795,027
Shares authorized (in shares)						0	7,400,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares						$ 0	$ 0.0001
Series D/D-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								1,395,936
Shares authorized (in shares)						0	5,787,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares						$ 0	$ 0.0001
Series C/C-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								1,507,906
Shares authorized (in shares)						0	6,032,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares						$ 0	$ 0.0001
Series B/B-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								2,246,744
Shares authorized (in shares)						0	9,596,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares						$ 0	$ 0.0001
Series A/A-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								1,856,998
Shares authorized (in shares)						0	7,528,000
Redeemable convertible preferred stock, par value (in usd per share) | $ / shares						$ 0	$ 0.0001
Additional Paid-In Capital
Temporary Equity [Line Items]
Issuance of common stock | $						$ 66,100
Additional Paid-In Capital | Series G Stock
Temporary Equity [Line Items]
Beneficial conversion feature of stock | $			$ 4,500
Common stock
Temporary Equity [Line Items]
Exercise of common stock warrants (in shares)						1,142,000
Issuance of Series G and Series G’ Stock (in shares)						5,821,000
Issuance of common stock | $						$ 1
Common stock | Series E/E-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								397,515
Common stock | Series B/B-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								2,121
Common stock | Series A/A-R Stock
Temporary Equity [Line Items]
Conversion of stock, shares issued (in shares)								12,375

REDEEMABLE CONVERTIBLE PREFER_5

REDEEMABLE CONVERTIBLE PREFERRED STOCK - Protective Provisions, Redemptions, Liquidation and Conversion (Details)	Dec. 31, 2018$ / shares
Series G’ Stock
Temporary Equity [Line Items]
Redemption price per share (in usd per share)	$ 34.4758
Liquidation of business payment per share (in usd per share)	34.4758
Liquidation preference (in usd per share)	$ 103.4274
Series G Stock
Temporary Equity [Line Items]
Percentage of approval required by outstanding instruments	66.60%
Redemption price per share (in usd per share)	$ 34.4758
Liquidation of business payment per share (in usd per share)	68.9516
Liquidation preference (in usd per share)	103.4274
Series F/F-R Stock
Temporary Equity [Line Items]
Redemption price per share (in usd per share)	58.40
Liquidation of business payment per share (in usd per share)	58.40
Liquidation preference (in usd per share)	175.20
Conversion price (in usd per share)	50.0568
Series E/E-R Stock
Temporary Equity [Line Items]
Redemption price per share (in usd per share)	37.7344
Liquidation of business payment per share (in usd per share)	37.7344
Liquidation preference (in usd per share)	113.2032
Conversion price (in usd per share)	37.7344
Series D/D-R Stock
Temporary Equity [Line Items]
Redemption price per share (in usd per share)	23.64
Liquidation of business payment per share (in usd per share)	23.64
Liquidation preference (in usd per share)	70.92
Conversion price (in usd per share)	23.64
Series C/C-R Stock
Temporary Equity [Line Items]
Redemption price per share (in usd per share)	12.2686
Liquidation of business payment per share (in usd per share)	21.4701
Liquidation preference (in usd per share)	36.8058
Conversion price (in usd per share)	12.2686
Series B/B-R Stock
Temporary Equity [Line Items]
Redemption price per share (in usd per share)	2.3567
Liquidation of business payment per share (in usd per share)	2.3567
Liquidation preference (in usd per share)	4.7134
Conversion price (in usd per share)	2.3567
Series A/A-R Stock
Temporary Equity [Line Items]
Redemption price per share (in usd per share)	1
Liquidation of business payment per share (in usd per share)	1
Liquidation preference (in usd per share)	2
Conversion price (in usd per share)	1
Series G Stock and G’ Stock
Temporary Equity [Line Items]
Conversion price (in usd per share)	$ 34.4758

COMMON STOCK WARRANTS - Warrant

COMMON STOCK WARRANTS - Warrant Activity (Details) - $ / shares	1 Months Ended		12 Months Ended
	Jun. 30, 2017	Jul. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Warrants outstanding, beginning balance (in shares)			110,000	110,000
Warrants outstanding, ending balance (in shares)			0	110,000	110,000
Common Stock Warrants
Shares
Warrants outstanding, beginning balance (in shares)			600,000	583,000	448,000
Granted (in shares)	17,500	97,125	644,000	17,000	97,000
Exercised (in shares)			(349,000)
Redeemable convertible preferred stock warrants converted to common stock warrants (in shares)			110,000		38,000
Forfeited/cancelled (in shares)			(138,000)
Warrants outstanding, ending balance (in shares)			867,000	600,000	583,000
Weighted-average exercise price per share
Warrants outstanding, beginning balance (in dollars per share)			$ 8.11	$ 7.52	$ 5.28
Granted (in dollars per share)	$ 27.68	$ 20	23.64	27.68	20
Exercised (in dollars per share)			4.69
Redeemable convertible preferred stock warrants converted to common stock warrants (in dollars per share)			12.16		1.92
Forfeited/cancelled (in dollars per share)			5.85
Warrants outstanding, ending balance (in dollars per share)			$ 21.89	$ 8.11	$ 7.52
Performance-based Warrants
Shares
Redeemable convertible preferred stock warrants converted to common stock warrants (in shares)			644,365

COMMON STOCK WARRANTS - Narrati

COMMON STOCK WARRANTS - Narrative (Details) - $ / shares	1 Months Ended		12 Months Ended
	Jun. 30, 2017	Jul. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 31, 2013
Class of Warrant or Right [Line Items]
Class of warrant (in shares)			0	110,000	110,000		644,365
Common Stock Warrants
Class of Warrant or Right [Line Items]
Class of warrant (in shares)			867,000	600,000	583,000	448,000
Warrants issued/granted (in shares)	17,500	97,125	644,000	17,000	97,000
Exercise price of warrants issued/granted (in dollars per share)	$ 27.68	$ 20	$ 23.64	$ 27.68	$ 20
Warrants converted (in shares)			110,000		38,000
Exercise price of warrants converted (in dollars per share)			$ 12.16		$ 1.92
Series A Common Stock Warrants
Class of Warrant or Right [Line Items]
Warrants converted (in shares)					12,500
Exercise price of warrants converted (in dollars per share)					$ 1
Series B Common Stock Warrants
Class of Warrant or Right [Line Items]
Warrants converted (in shares)					25,000
Exercise price of warrants converted (in dollars per share)					$ 2.36
Performance-based Warrants
Class of Warrant or Right [Line Items]
Warrants converted (in shares)			644,365
Class of warrant , unvested (in shares)					644,365
Series E Common Stock Warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants converted (in dollars per share)					$ 23.64

FAIR VALUE MEASUREMENTS - Finan

FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Jul. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability	$ 0	$ 10,230
Total liabilities		10,230
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities		0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities		0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities		10,230
Preferred Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		2,285
Preferred Stock Warrants | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		0
Preferred Stock Warrants | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		0
Preferred Stock Warrants | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		2,285
Common Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		7,945	$ 300	$ 1,000
Common Stock Warrants | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		0
Common Stock Warrants | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		0
Common Stock Warrants | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term warrant liability		$ 7,945

FAIR VALUE MEASUREMENTS - Instr

FAIR VALUE MEASUREMENTS - Instruments Recorded at Fair Value Using Level 3 Inputs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Preferred Stock Warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 2,285	$ 2,197	$ 2,942
Exercise/Conversion to common stock	(1,736)		(777)
Changes in fair value	(549)	88	32
Fair value, ending balance	0	2,285	2,197
Common Stock Warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	7,945	0
Exercise/Conversion to common stock	(15,254)
Issuance of stock		7,452
Changes in fair value	7,309	493
Fair value, ending balance	0	7,945	0
Convertible Promissory Notes
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	0	72,332	0
Exercise/Conversion to common stock			66,391
Accrued interest on convertible promissory notes		1,701	2,876
Changes in fair value	0	(4,969)	3,065
Fair value, ending balance	$ 0	0	$ 72,332
Convertible Promissory Notes | Series G’ Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Exercise/Conversion to common stock		(44,672)
Convertible Promissory Notes | Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Exercise/Conversion to common stock		$ (24,392)

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value Assumptions (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cost of Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input		0
Cost of Debt | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input			0.12
Cost of Debt | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input			0.17
Cost of Equity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input		0
Cost of Equity | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input			0.24
Cost of Equity | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input			0.26
Weighted-average cost of capital applicable to preferred stock warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input		0.205	0.232
Discount for lack of marketability | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.07	0.07	0.08
Discount for lack of marketability | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.13	0.13	0.12
Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input		0.55	0.54
Risk-free interest rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.012	0.012	0.007
Risk-free interest rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.014	0.014	0.012

FAIR VALUE MEASUREMENTS - Prefe

FAIR VALUE MEASUREMENTS - Preferred Stock Warrants (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2013
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)				$ 23.64
Class of warrant (in shares)	0	110,000	110,000	644,365
Series B/B-R Stock | Grant One
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)	$ 2.36
Class of warrant (in shares)	0	59,000	59,000
Series D/D-R Stock | Grant One
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)	$ 23.64
Class of warrant (in shares)	0	38,000	38,000
Series D/D-R Stock | Grant Two
Class of Stock [Line Items]
Exercise price of warrants (in usd per share)	$ 23.64
Class of warrant (in shares)	0	13,000	13,000

FAIR VALUE MEASUREMENTS - Narra

FAIR VALUE MEASUREMENTS - Narrative (Details) $ / shares in Units, $ in Thousands	Aug. 08, 2018$ / shares	Aug. 31, 2018USD ($)$ / sharesshares	Feb. 28, 2018USD ($)	May 31, 2017USD ($)$ / sharesshares	May 31, 2013$ / sharesshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Feb. 08, 2018$ / shares	Jun. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2016$ / shares	Jul. 31, 2016USD ($)$ / sharesshares	May 26, 2016shares	Apr. 30, 2016$ / shares	Dec. 31, 2015USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)									$ 13
Fair value of warrants issued | $						$ 0	$ 10,230
Shares issued (in shares) | shares						22,466,000	3,439,000
Exercise price of warrants (in usd per share)					$ 23.64
Change in fair value of warrant liabilities, net | $						$ (6,760)	$ (581)	$ (32)
Class of warrant (in shares) | shares					644,365	0	110,000	110,000
Warrant, term					10 years
Common Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)										$ 30.08		$ 17.92
Fair value of warrants issued | $							$ 7,945			$ 300		$ 1,000
Exercise price of warrants (in usd per share)										$ 27.68		$ 20
Liability value | $						$ 0	7,945	$ 0
Class of warrant (in shares) | shares										17,500		97,125
Stock option expense | $			$ 2,500
Preferred Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of warrants issued | $							2,285
Liability value | $						0	2,285	2,197							$ 2,942
Convertible Promissory Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability value | $						$ 0	$ 0	$ 72,332							$ 0
Series B Stock Warrants [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants converted (in shares) | shares													25,000
Series B Stock Warrants [Member] | Preferred Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)											$ 18.16			$ 20.48
Conversion date fair value per share (in usd per share)								$ 20.36
Series E Stock Warrants [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants converted (in shares) | shares													644,365
Series A Stock Warrants [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants converted (in shares) | shares													12,500
Series A Stock Warrants [Member] | Preferred Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)														$ 21.56
Conversion date fair value per share (in usd per share)								$ 21.44
Series B/B-R Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)							$ 26.8		20.18
Conversion of securities to common stock (in shares) | shares						2,247,000		2,000
Series D/D-R Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value per share (in usd per share)							$ 13.63		$ 10.57
Conversion of securities to common stock (in shares) | shares						1,396,000		0
Series G Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Shares issued (in shares) | shares				346,334
Class of warrant, numerator input value (in usd per share)				$ 68.9516
Number of trading days				30 days
Number of days following prospectus	180 days
Exercise price of warrants (in usd per share)	$ 0.0004	$ 0.0004
Liability value | $				$ 7,500
Exercise of common stock warrants (in shares) | shares		792,434
Conversion of securities to common stock (in shares) | shares		792,434				346,000
Issuance of stock | $		$ 15,300		$ 11,900
Change in fair value of warrant liabilities, net | $						$ 7,300	$ 500
Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant inputs									0.5
Volatility | Common Stock Warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant inputs										0.5		0.51
Volatility | Series G Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant inputs				0.59
Discount for lack of marketability | Series G Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Significant inputs					0.11

FAIR VALUE MEASUREMENTS - Warra

FAIR VALUE MEASUREMENTS - Warrants Pricing Model (Details)	Feb. 08, 2018$ / shares	Jun. 30, 2017$ / shares	Jul. 31, 2016$ / shares	Dec. 31, 2018$ / shares	Dec. 31, 2017$ / shares	Dec. 31, 2016$ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted-average grant date fair value (in usd per share)	$ 3.91			$ 10	$ 12.11	$ 7
Value of common stock (in usd per share)	$ 13
Expected term	5 years 3 months 18 days
Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant inputs	0.5
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant inputs	0.020
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant inputs	0
Common Stock Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted-average grant date fair value (in usd per share)		$ 19.04	$ 10.44
Value of common stock (in usd per share)		$ 30.08	$ 17.92
Expected term		10 years	10 years
Common Stock Warrants | Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant inputs		0.5	0.51
Common Stock Warrants | Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant inputs		0.022	0.012
Common Stock Warrants | Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant inputs		0	0

RELATED PARTIES - Narrative (De

RELATED PARTIES - Narrative (Details) - USD ($)	1 Months Ended			12 Months Ended
	Feb. 28, 2018	May 31, 2017	May 31, 2013	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2018	Aug. 08, 2018
Related Party Transaction [Line Items]
Individuals holding, capital stock, percentage threshold				5.00%
Proceeds from issuance of preferred stock				$ 0	$ 11,940,000	$ 0
Issuance of Series G and Series G’ Stock (in shares)					1,296,000
Conversion of stock, shares converted (in shares)		801,329
Warrant, term			10 years
Class of warrant (in shares)			644,365	0	110,000	110,000
Exercise price of warrants (in usd per share)			$ 23.64
Series G Stock
Related Party Transaction [Line Items]
Proceeds from issuance of preferred stock		$ 11,900,000
Issuance of Series G and Series G’ Stock (in shares)		346,334			346,000
Exercise price of warrants (in usd per share)							$ 0.0004	$ 0.0004
Series G’ Stock
Related Party Transaction [Line Items]
Conversion of stock, shares converted (in shares)		1,295,746
Series E
Related Party Transaction [Line Items]
Issuance of Series G and Series G’ Stock (in shares)			397,515
Common Stock Warrants
Related Party Transaction [Line Items]
Stock option expense	$ 2,500,000
Stockholders' Equity | Shareholder Concentration Risk
Related Party Transaction [Line Items]
Concentration risk				5.00%
Convertible Debt [Member]
Related Party Transaction [Line Items]
Debt instrument, face amount				$ 50,700,000
Convertible Debt [Member] | Affiliated Entity
Related Party Transaction [Line Items]
Debt instrument, face amount				$ 27,000,000

RELATED PARTIES - Convertible P

RELATED PARTIES - Convertible Promissory Notes (Details) - Purchase transaction of convertible promissory notes	Dec. 31, 2016USD ($)
Scott D. Grimes
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	$ 650,000
Lynne M. Laube
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	350,000
Aeroplan Holdings Europe Sàrl | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	3,987,000
Polaris Venture Partners | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	5,321,000
Canaan VIII L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	6,514,000
Discovery Capital | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	2,663,000
Polaris Venture Partners V, L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	5,134,443.03
Polaris Venture Partners Entrepreneurs’ Fund V, L.L. | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	100,069.82
Polaris Venture Partners Founders’ Fund V, L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	35,170.61
Polaris Venture Partners Special Founders’ Fund V, L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	51,344.45
Discovery Global Opportunity Master Fund, Ltd. | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	2,385,974.51
Discovery Global Focus Master Fund, Ltd. | Affiliated Entity
Related Party Transaction [Line Items]
Due to directors, executive offers and stockholders	$ 277,291.57

RELATED PARTIES - Series G _ Se

RELATED PARTIES - Series G / Series G’ (Details) - $ / shares	1 Months Ended
	May 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2013
Related Party Transaction [Line Items]
Shares outstanding (in shares)		22,466,000	3,439,000
Class of warrant (in shares)		0	110,000	110,000	644,365
Series G Stock
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0	346,000	0
Class of warrant, numerator input value (in usd per share)	$ 68.9516
Number of trading days	30 days
Series G’ Stock
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0	1,296,000	0
Aimia Inc. | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		801,000
Class of warrant (in shares)		0
Aimia Inc. | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Aimia Inc. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		382,000
Polaris Venture Partners | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		66,000
Polaris Venture Partners | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		29,000
Polaris Venture Partners | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		212,000
Canaan VIII L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		123,000
Canaan VIII L.P. | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		54,000
Canaan VIII L.P. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		260,000
Discovery Capital | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		0
Discovery Capital | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Discovery Capital | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		106,000
Scott D. Grimes | Scott D. Grimes
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		0
Scott D. Grimes | Series G Stock | Scott D. Grimes
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Scott D. Grimes | Series G’ Stock | Scott D. Grimes
Related Party Transaction [Line Items]
Shares outstanding (in shares)		26,000
Lynne M. Laube | Lynne M. Laube
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		0
Lynne M. Laube | Series G Stock | Lynne M. Laube
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Lynne M. Laube | Series G’ Stock | Lynne M. Laube
Related Party Transaction [Line Items]
Shares outstanding (in shares)		14,000
Entities affiliated with Mark A. Johnson | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		80,000
Entities affiliated with Mark A. Johnson | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		35,000
Entities affiliated with Mark A. Johnson | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		15,000
Mark A. Johnson | Affiliated Entity
Related Party Transaction [Line Items]
Class of warrant (in shares)		13,273
Mark A. Johnson | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		5,801
John Klinck | Director
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		13,000
John Klinck | Series G Stock | Director
Related Party Transaction [Line Items]
Shares outstanding (in shares)		6,000
John Klinck | Series G’ Stock | Director
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
David Adams | Director
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Class of warrant (in shares)		7,000
David Adams | Series G Stock | Director
Related Party Transaction [Line Items]
Shares outstanding (in shares)		3,000
David Adams | Series G’ Stock | Director
Related Party Transaction [Line Items]
Shares outstanding (in shares)		0
Aeroplan Holdings Europe Sàrl | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		159,207
Aimia EMEA Limited | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		801,329
Aimia EMEA Limited | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		223,020
Polaris Venture Partners V, L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Class of warrant (in shares)		64,038
Polaris Venture Partners V, L.P. | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		27,988
Polaris Venture Partners V, L.P. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		205,020
Polaris Venture Partners Entrepreneurs’ Fund V, L.L. | Affiliated Entity
Related Party Transaction [Line Items]
Class of warrant (in shares)		1,247
Polaris Venture Partners Entrepreneurs’ Fund V, L.L. | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		545
Polaris Venture Partners Entrepreneurs’ Fund V, L.L. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		3,995
Polaris Venture Partners Founders’ Fund V, L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Class of warrant (in shares)		438
Polaris Venture Partners Founders’ Fund V, L.P. | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		191
Polaris Venture Partners Founders’ Fund V, L.P. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		1,404
Polaris Venture Partners Special Founders’ Fund V, L.P. | Affiliated Entity
Related Party Transaction [Line Items]
Class of warrant (in shares)		641
Polaris Venture Partners Special Founders’ Fund V, L.P. | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		280
Polaris Venture Partners Special Founders’ Fund V, L.P. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		2,050
Discovery Opportunity Master Fund, Ltd. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		95,272
Discovery Global Opportunity Master Fund, Ltd. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		11,072
TTP Fund II, L.P. | Series G’ Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		15,045
TTV Ivy Holdings, LLC | Affiliated Entity
Related Party Transaction [Line Items]
Class of warrant (in shares)		66,365
TTV Ivy Holdings, LLC | Series G Stock | Affiliated Entity
Related Party Transaction [Line Items]
Shares outstanding (in shares)		29,005

RELATED PARTIES - Agreements wi

RELATED PARTIES - Agreements with Aimia Inc. and Affiliated Entities (Details) - Cooperation Agreement - Aimia EMEA Limited - Affiliated Entity $ in Millions	1 Months Ended
	Jun. 30, 2016USD ($)
Related Party Transaction [Line Items]
Amounts of transaction	$ 22.3
Payable to related party	$ 5.7

VARIABLE INTEREST ENTITY (Detai

VARIABLE INTEREST ENTITY (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Delivery costs	$ 10,632	$ 7,012	$ 6,127
Sales and marketing expense	41,878	31,927	31,261
General and administration expense	34,228	20,100	21,355
Allocation of revenue less FI Share and other third-party costs	150,684	130,365	112,821
Net cash used in operating activities	(18,995)	(22,102)	(32,498)
Net cash used in investing activities	$ (7,342)	$ (1,647)	(2,545)
Cardlytics UK
Variable Interest Entity [Line Items]
Ownership percentage	100.00%
Expenses absorbed	50.00%
Expenses absorbed, information technology and systems support	100.00%
Net cash used in operating activities			600
Net cash used in investing activities			$ 0
Aimia Inc. | Cardlytics UK
Variable Interest Entity [Line Items]
Delivery costs	$ 24
Sales and marketing expense	597
General and administration expense	129
Allocation of revenue less FI Share and other third-party costs	$ 1,223

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Financial institution partners, payments to partners, not yet earned			$ 5,300,000
Decrease to FI share liability			(3,742,000)	$ (804,000)	$ (8,482,000)
Deferred FI cost, impairment loss			0	$ 0	$ 814,000
Required payment for not meeting minimum FI Share commitment	$ 2,600,000
Financial Institution Share Commitment
Loss Contingencies [Line Items]
FI share commitment			$ 10,000,000
Forecast
Loss Contingencies [Line Items]
Decrease to FI share liability		$ 4,600,000

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Deferred FI Implementation Costs (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Financial Institution Costs [Roll Forward]
Beginning balance	$ 13,625,000	$ 8,451,000	$ 1,936,000
Deferred costs	9,250,000	10,900,000	8,205,000
Recoveries through FI Share	(5,380,000)	(4,100,000)	0
Amortization	(1,618,000)	(1,626,000)	(876,000)
Deferred FI cost, impairment loss	0	0	814,000
Ending balance	$ 15,877,000	$ 13,625,000	$ 8,451,000

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Payments to FI Partners (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,019	$ 3,744
2,020	3,628
2,021	3,245
Total	$ 10,617

COMMITMENTS AND CONTINGENCIES_4

COMMITMENTS AND CONTINGENCIES - Operating Leases (Details) $ in Thousands, £ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2016GBP (£)ft²	Jul. 31, 2015USD ($)	Aug. 31, 2013USD ($)ft²
Property Subject to or Available for Operating Lease [Line Items]
Operating leases, rent expense	$ 2,900	$ 3,000	$ 3,000
2,019	2,706
2,020	2,089
2,021	1,654
2,022	1,703
2,023	1,755
Thereafter	2,418
Total	$ 12,325
Corporate Headquarters, Atlanta, GA
Property Subject to or Available for Operating Lease [Line Items]
Lease, term of contract						130 months
Area of real estate property (sq ft) | ft²						76,880
Tenant improvement allowance						$ 3,800
Total						$ 16,000
Data Center Space, Atlanta, GA
Property Subject to or Available for Operating Lease [Line Items]
Lease, term of contract					60 months
Total					$ 2,300
Office, Victoria, London
Property Subject to or Available for Operating Lease [Line Items]
Lease, term of contract				40 months
Area of real estate property (sq ft) | ft²				5,295
Total | £				£ 0.8

COMMITMENTS AND CONTINGENCIES_5

COMMITMENTS AND CONTINGENCIES - Letters of Credit (Details) - USD ($) $ in Millions	May 31, 2018	May 31, 2017	Dec. 31, 2016	Apr. 01, 2014
Commitments and Contingencies Disclosure [Abstract]
Letters of credit outstanding	$ 1	$ 1.5	$ 2	$ 2.5

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Redeemable convertible preferred stock | Series A/A-R Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	1,857	1,857
Redeemable convertible preferred stock | Series B/B-R Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	2,247	2,247
Redeemable convertible preferred stock | Series C/C-R Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	1,508	1,508
Redeemable convertible preferred stock | Series D/D-R Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	1,396	1,396
Redeemable convertible preferred stock | Series E/E-R Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	795	795
Redeemable convertible preferred stock | Series F/F-R Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	1,199	1,199
Redeemable convertible preferred stock | Series G Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	346	0
Redeemable convertible preferred stock | Series G’ Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	1,296	0
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	1,774	2,514	2,137
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	867	1,245	1,227
Common stock warrants | Series G’ Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	547	0
Redeemable convertible preferred stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	110	110
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	381	0	0
Restricted securities units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	37	53
Convertible promissory notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0	0	2,734
Common stock issuable pursuant to the ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	36	0	0

SEGMENTS - Narrative (Details)

SEGMENTS - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	3
Capital expenditures	$ 5,920	$ 1,215	$ 1,827
United Kingdom
Segment Reporting Information [Line Items]
Capital expenditures		$ 300	$ 100

SEGMENTS - Revenue by Segment (

SEGMENTS - Revenue by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Adjusted contribution	$ 69,450	$ 58,744	$ 48,226
Plus: FI Share and other third-party costs	81,234	71,621	64,595
Revenues	150,684	130,365	112,821
FI Share, shortfall expense	0	0	2,600
Non-cash gain on financial institution share	800
Cardlytics Direct
Segment Reporting Information [Line Items]
Adjusted contribution	69,364	55,184	41,374
Plus: FI Share and other third-party costs	79,959	67,207	56,415
Revenues	149,323	122,391	97,789
Other Platform Solutions
Segment Reporting Information [Line Items]
Adjusted contribution	86	3,560	6,852
Plus: FI Share and other third-party costs	1,275	4,414	8,180
Revenues	$ 1,361	$ 7,974	$ 15,032

SEGMENTS - Adjusted Contributio

SEGMENTS - Adjusted Contribution Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Adjusted contribution	$ 69,450	$ 58,744	$ 48,226
Non-cash equity expense included in FI Share	2,519	0	0
Amortization and impairment of deferred FI implementation costs	1,618	1,626	1,690
Delivery costs	10,632	7,012	6,127
Sales and marketing expense	41,878	31,927	31,261
Research and development expense	16,210	12,150	13,902
General and administration expense	34,228	20,100	21,355
Depreciation and amortization expense	3,282	3,028	4,219
Termination of U.K. agreement expense	0	0	25,904
Total other expense	12,125	2,542	19,464
Loss before income taxes	$ (53,042)	$ (19,641)	$ (75,696)

SEGMENTS - Geographical Informa

SEGMENTS - Geographical Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 150,684	$ 130,365	$ 112,821
Property and equipment	10,230	7,319
United States
Segment Reporting Information [Line Items]
Revenues	131,563	113,509	100,590
Property and equipment	9,794	6,813
United Kingdom
Segment Reporting Information [Line Items]
Revenues	19,121	16,856	$ 12,231
Property and equipment	$ 436	$ 506