DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying interim condensed consolidated financial statements of the Company are unaudited. These interim condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP) and the applicable rules and regulations of the Securities and Exchange Commission (SEC) for interim financial information. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The December 31, 2018 condensed consolidated balance sheet was derived from the audited financial statements as of that date, but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The accompanying unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and, in the opinion of management, reflect all adjustments of a normal recurring nature considered necessary to state fairly the Company's consolidated financial position, results of operations, comprehensive income (loss), and cash flows for the interim periods. All intercompany transactions and balances have been eliminated in consolidation. The interim results for the three and nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019, or for any other future annual or interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Consolidated Financial Statements and related notes in the Company's Annual Report on Form 10-K for the year ended December 31, 2018.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses, as well as related disclosure of contingent assets and liabilities. Actual results could differ from the Company’s estimates. To the extent that there are material differences between these estimates and actual results, the Company’s financial condition or operating results will be materially affected. The Company bases its estimates on past experience and other assumptions that the Company believes are reasonable under the circumstances, and the Company evaluates these estimates on an ongoing basis. Estimates, judgments, and assumptions in these consolidated financial statements include, but are not limited to, those related to revenue recognition, accrued transaction losses, valuation of the debt component of convertible senior notes, valuation of loans held for sale, goodwill, acquired intangible assets and deferred revenue, income and other taxes, operating and financing lease right-of-use assets and related liabilities, and share-based compensation.
Concentration of Credit Risk	Concentration of Credit Risk For the three and nine months ended September 30, 2019 and 2018, the Company had no customer that accounted for greater than 10% of total net revenue. The Company had three third-party payment processors that represented approximately 46%, 34%, and 9% of settlements receivable as of September 30, 2019. The same three parties represented approximately 45%, 33%, and 9% of settlements receivable as of December 31, 2018. All other third-party processors were insignificant. Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents, restricted cash, marketable debt securities, settlements receivables, customer funds, and loans held for sale. The associated risk of concentration for cash and cash equivalents and restricted cash is mitigated by banking with creditworthy institutions. At certain times, amounts on deposit exceed federal deposit insurance limits. The associated risk of concentration for marketable debt securities is mitigated by holding a diversified portfolio of highly rated investments. Settlements receivable are amounts due from well-established payment processing companies and normally take one or two business days to settle which mitigates the associated risk of concentration. The associated risk of concentration for loans held for sale is partially mitigated by credit evaluations that are performed prior to facilitating the offering of loans and ongoing performance monitoring of the Company’s loan customers.
Assets Held for Sale	Assets Held for Sale The Company classifies an asset group (‘asset’) as held for sale in the period that (i) it has approved and committed to a plan to sell the asset, (ii) the asset is available for immediate sale in its present condition, (iii) an active program to locate a buyer and other actions required to sell the asset have been initiated, (iv) the sale of the asset is probable and transfer of the asset is expected to qualify for recognition as a completed sale within one year (subject to certain events or circumstances), (v) the asset is being actively marketed for sale at a price that is reasonable in relation to its current fair value, and (vi) it is unlikely that significant changes to the plan will be made or that the plan will be withdrawn. The Company initially and subsequently measures a long-lived asset that is classified as held for sale at the lower of its carrying value or fair value less any costs to sell. Any loss resulting from this measurement is recognized in general and administrative expenses in the period in which the held for sale criteria are met. Conversely, gains are generally not recognized on the sale of a long-lived asset until the date of sale. Upon designation as an asset held for sale, the Company stops recording depreciation or amortization expense on the asset. The Company assesses the fair value of assets held for sale less any costs to sell at each reporting period until the asset is no longer classified as held for sale.
New Accounting Policies and Recent Accounting Pronouncements	New Accounting Policies The Company adopted Accounting Standards Codification (ASC) 842, Leases on January 1, 2019, and elected the optional transition method to apply the transition provisions from the effective date of adoption, which requires the Company to report the cumulative effect of the adoption of the standard on the date of adoption with no changes to the prior period balances. Pursuant to the practical expedients, the Company has elected not to reassess: (i) whether expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases, or, (iii) initial direct costs for any existing leases. The Company recognized $112.0 million of operating right-of-use lease assets and $135.6 million of operating lease liabilities on its consolidated balance sheet upon adoption of this standard. Additionally, the Company derecognized $149 million related to the build-to-suit asset and liability upon adoption of this standard because the Company is no longer deemed to be the owner of the related asset under construction under the new standard. Refer to Note 19 for further detail. Except for the adoption of ASC 842, there have been no material changes to the Company’s accounting policies during the nine months ended September 30, 2019, as compared to the accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. Recent Accounting Pronouncements Recently issued accounting pronouncements not yet adopted In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13,Financial Instruments - Credit Losses, which requires the measurement and recognition of expected credit losses for financial assets held. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available for sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. This guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. The Company intends to adopt this guidance effective January 1, 2020. The Company’s preliminary conclusion is that the new guidance will not have a material impact on the balances reported on its consolidated financial statements. The Company has also determined that allowances for credit losses associated with its available for sale debt securities would be immaterial. Upon adoption of this guidance, the Company will expand its disclosures to discuss how it develops its expected credit loss estimates, the methodology applied to estimate the allowance for credit losses, and the factors that influence the Company's estimates. For available for sale debt securities with unrealized losses where the Company concludes that an allowance for credit losses is not necessary, the Company will expand its disclosures of the associated fair value of such securities as well as the basis for conclusions that an allowance for credit losses was not necessary. In January 2017, the FASB issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment. The new guidance eliminates the requirement to calculate the implied fair value of goodwill assuming a hypothetical purchase price allocation (i.e., Step 2 of the goodwill impairment test) to measure a goodwill impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value, not to exceed the carrying amount of goodwill. This standard should be adopted when the Company performs its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019, with early adoption permitted. The amendments should be applied on a prospective basis. The Company intends to adopt this guidance effective with its 2019 annual goodwill impairment test which it performs as of December 31. The Company does not expect the adoption of this guidance to have a material impact on the consolidated financial statements and related disclosures. In July 2018, the FASB issued ASU 2018-13, Changes to the Disclosure Requirements for Fair Value Measurement, which will remove, modify, and add disclosure requirements for fair value measurements to improve the overall usefulness of such disclosures. This guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted for any removed or modified disclosure requirements. Transition is on a prospective basis for the new and modified disclosures, and on a retrospective basis for disclosures that have been eliminated. The Company currently does not intend to early adopt any portion of this disclosure guidance. The Company is currently evaluating the impact this guidance may have on the consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which is intended to align the requirements for capitalization of implementation costs incurred in a cloud computing arrangement that is a service contract with the existing guidance for internal-use software. This guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted. The guidance provides flexibility in adoption, allowing for either retrospective adjustment or prospective adjustment for all implementation costs incurred after the date of adoption. The Company does not expect the adoption of this guidance to have a material impact on the consolidated financial statements and related disclosures.

DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

9 Months Ended

Sep. 30, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The accompanying interim condensed consolidated financial statements of the Company are unaudited. These interim condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP) and the applicable rules and regulations of the Securities and Exchange Commission (SEC) for interim financial information. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The December 31, 2018 condensed consolidated balance sheet was derived from the audited financial statements as of that date, but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements.

The accompanying unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and, in the opinion of management, reflect all adjustments of a normal recurring nature considered necessary to state fairly the Company's consolidated financial position, results of operations, comprehensive income (loss), and cash flows for the interim periods. All intercompany transactions and balances have been eliminated in consolidation. The interim results for the three and nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019, or for any other future annual or interim period.

The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Consolidated Financial Statements and related notes in the Company's Annual Report on Form 10-K for the year ended December 31, 2018.

Use of Estimates

The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses, as well as related disclosure of contingent assets and liabilities. Actual results could differ from the Company’s estimates. To the extent that there are material differences between these estimates and actual results, the Company’s financial condition or operating results will be materially affected. The Company bases its estimates on past experience and other assumptions that the Company believes are reasonable under the circumstances, and the Company evaluates these estimates on an ongoing basis.

Estimates, judgments, and assumptions in these consolidated financial statements include, but are not limited to, those related to revenue recognition, accrued transaction losses, valuation of the debt component of convertible senior notes, valuation of loans held for sale, goodwill, acquired intangible assets and deferred revenue, income and other taxes, operating and financing lease right-of-use assets and related liabilities, and share-based compensation.

Concentration of Credit Risk

For the three and nine months ended September 30, 2019 and 2018, the Company had no customer that accounted for greater than 10% of total net revenue.

The Company had three third-party payment processors that represented approximately 46%, 34%, and 9% of settlements receivable as of September 30, 2019. The same three parties represented approximately 45%, 33%, and 9% of settlements receivable as of December 31, 2018. All other third-party processors were insignificant.

Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents, restricted cash, marketable debt securities, settlements receivables, customer funds, and loans held for sale. The associated risk of concentration for cash and cash equivalents and restricted cash is mitigated by banking with creditworthy institutions. At certain times, amounts on deposit exceed federal deposit insurance limits. The associated risk of concentration for marketable debt securities is mitigated by holding a diversified portfolio of highly rated investments. Settlements receivable are amounts due from well-established payment processing companies and normally take one or two business days to settle which mitigates the associated risk of concentration. The associated risk of concentration for loans held for sale is partially mitigated by credit evaluations that are performed prior to facilitating the offering of loans and ongoing performance monitoring of the Company’s loan customers.

Assets Held for Sale

The Company classifies an asset group (‘asset’) as held for sale in the period that (i) it has approved and committed to a plan to sell the asset, (ii) the asset is available for immediate sale in its present condition, (iii) an active program to locate a buyer and other actions required to sell the asset have been initiated, (iv) the sale of the asset is probable and transfer of the asset is expected to qualify for recognition as a completed sale within one year (subject to certain events or circumstances), (v) the asset is being actively marketed for sale at a price that is reasonable in relation to its current fair value, and (vi) it is unlikely that significant changes to the plan will be made or that the plan will be withdrawn. The Company initially and subsequently measures a long-lived asset that is classified as held for sale at the lower of its carrying value or fair value less any costs to sell. Any loss resulting from this measurement is recognized in general and administrative expenses in the period in which the held for sale criteria are met. Conversely, gains are generally not recognized on the sale of a long-lived asset until the date of sale. Upon designation as an asset held for sale, the Company stops recording depreciation or amortization expense on the asset. The Company assesses the fair value of assets held for sale less any costs to sell at each reporting period until the asset is no longer classified as held for sale.

New Accounting Policies and Recent Accounting Pronouncements

New Accounting Policies

The Company adopted Accounting Standards Codification (ASC) 842, Leases on January 1, 2019, and elected the optional transition method to apply the transition provisions from the effective date of adoption, which requires the Company to report the cumulative effect of the adoption of the standard on the date of adoption with no changes to the prior period balances. Pursuant to the practical expedients, the Company has elected not to reassess: (i) whether expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases, or, (iii) initial direct costs for any existing leases. The Company recognized $112.0 million of operating right-of-use lease assets and $135.6 million of operating lease liabilities on its consolidated balance sheet upon adoption of this standard. Additionally, the Company derecognized $149 million related to the build-to-suit asset and liability upon adoption of this standard because the Company is no longer deemed to be the owner of the related asset under construction under the new standard. Refer to Note 19 for further detail.

Except for the adoption of ASC 842, there have been no material changes to the Company’s accounting policies during the nine months ended September 30, 2019, as compared to the accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.

Recent Accounting Pronouncements

Recently issued accounting pronouncements not yet adopted

In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13,Financial Instruments - Credit Losses, which requires the measurement and recognition of expected credit losses for financial assets held. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available for sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. This guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. The Company intends to adopt this guidance effective January 1, 2020. The Company’s preliminary conclusion is that the new guidance will not have a material impact on the balances reported on its consolidated financial statements. The Company has also determined that allowances for credit losses associated with its available for sale debt securities would be immaterial. Upon adoption of this guidance, the Company will expand its disclosures to discuss how it develops its expected credit loss estimates, the methodology applied to estimate the allowance for credit losses, and the factors that influence the Company's estimates. For available for sale debt securities with unrealized losses where the Company

concludes that an allowance for credit losses is not necessary, the Company will expand its disclosures of the associated fair value of such securities as well as the basis for conclusions that an allowance for credit losses was not necessary.

In January 2017, the FASB issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment. The new guidance eliminates the requirement to calculate the implied fair value of goodwill assuming a hypothetical purchase price allocation (i.e., Step 2 of the goodwill impairment test) to measure a goodwill impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value, not to exceed the carrying amount of goodwill. This standard should be adopted when the Company performs its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019, with early adoption permitted. The amendments should be applied on a prospective basis. The Company intends to adopt this guidance effective with its 2019 annual goodwill impairment test which it performs as of December 31. The Company does not expect the adoption of this guidance to have a material impact on the consolidated financial statements and related disclosures.

In July 2018, the FASB issued ASU 2018-13, Changes to the Disclosure Requirements for Fair Value Measurement, which will remove, modify, and add disclosure requirements for fair value measurements to improve the overall usefulness of such disclosures. This guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted for any removed or modified disclosure requirements. Transition is on a prospective basis for the new and modified disclosures, and on a retrospective basis for disclosures that have been eliminated. The Company currently does not intend to early adopt any portion of this disclosure guidance. The Company is currently evaluating the impact this guidance may have on the consolidated financial statements and related disclosures.

In August 2018, the FASB issued ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which is intended to align the requirements for capitalization of implementation costs incurred in a cloud computing arrangement that is a service contract with the existing guidance for internal-use software. This guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted. The guidance provides flexibility in adoption, allowing for either retrospective adjustment or prospective adjustment for all implementation costs incurred after the date of adoption. The Company does not expect the adoption of this guidance to have a material impact on the consolidated financial statements and related disclosures.