Groupon (GRPN) 10-Q 3 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Aug. 01, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Groupon, Inc.
Entity Central Index Key	1,490,281
Entity Filer Category	Large Accelerated Filer
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Entity Common Stock, Shares Outstanding		568,395,979

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents		$ 662,893	$ 880,129
Accounts receivable, net		76,302	98,294
Prepaid expenses and other current assets (including $8,517 and $0 at June 30, 2018 and December 31, 2017, respectively, at fair value)		104,524	94,025
Total current assets		843,719	1,072,448
Property, equipment and software, net		148,450	151,145
Goodwill		328,799	286,989
Intangible assets, net		37,075	19,196
Investments (including $86,578 and $109,751 at June 30, 2018 and December 31, 2017, respectively, at fair value)		109,606	135,189
Other non-current assets		21,051	12,538
Total Assets	[1]	1,488,700	1,677,505
Current liabilities:
Accounts payable		23,026	31,968
Accrued merchant and supplier payables		528,224	770,335
Accrued expenses and other current liabilities		367,519	331,196
Total current liabilities		918,769	1,133,499
Convertible senior notes, net		195,559	189,753
Other non-current liabilities		103,235	102,408
Total Liabilities		1,217,563	1,425,660
Commitments and contingencies (see Note 8)
Stockholders' Equity
Common stock, par value $0.0001 per share, 2,010,000,000 shares authorized; 755,806,627 shares issued and 567,204,385 shares outstanding at June 30, 2018; 748,541,862 shares issued and 559,939,620 shares outstanding at December 31, 2017		76	75
Additional paid-in capital		2,206,741	2,174,708
Treasury stock, at cost, 188,602,242 shares at June 30, 2018 and December 31, 2017		(867,450)	(867,450)
Accumulated deficit		(1,101,342)	(1,088,204)
Accumulated other comprehensive income (loss)		32,307	31,844
Total Groupon, Inc. Stockholders' Equity		270,332	250,973
Noncontrolling interests		805	872
Total Equity		271,137	251,845
Total Liabilities and Equity		$ 1,488,700	$ 1,677,505
[1]	(1)North America contains assets from the United States of $846.3 million and $1,006.2 million as of June 30, 2018 and December 31, 2017, respectively. International contains assets from Ireland of $162.7 million and $219.7 million as of June 30, 2018 and December 31, 2017, respectively. There were no other individual countries that represented more than 10% of consolidated total assets as of June 30, 2018 and December 31, 2017.

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Investments, Current, Fair Value Disclosure	$ 8,517	$ 0
Investments at fair value	$ 86,578	$ 109,751
Common stock, par value (in usd per share)	$ 4.30
Common Stock
Common stock, par value (in usd per share)	$ 0.1000	$ 0.1000
Common Stock, Shares Authorized	2,010,000,000,000	2,010,000,000,000
Common Stock, Shares, Issued	755,806,627,000	748,541,862,000
Common Stock, Shares, Outstanding	567,204,385,000	559,939,620,000
Treasury Stock
Treasury Stock, Shares	(188,602,242)	(188,602,242)

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017
Revenue:
Service		$ 295,652	[1]	$ 315,854	$ 597,449	[1]	$ 617,426
Product		321,744		346,765	646,487		718,819
Total revenue		617,396	[2]	662,619	1,243,936	[2]	1,336,245
Cost of revenue:
Service		30,230	[3]	38,478	61,375	[3]	81,351
Product		263,508		296,074	534,018		617,376
Total cost of revenue		293,738	[3]	334,552	595,393	[3]	698,727
Gross profit		323,658		328,067	648,543		637,518
Operating expenses:
Marketing		94,178	[4]	100,658	193,334	[4]	187,000
Selling, general and administrative		294,124	[5]	230,223	516,185	[5]	462,281
Restructuring charges		(399)		4,584	(116)		7,315
Total operating expenses		387,903		335,465	709,403		656,596
Income (loss) from operations	[6],[7]	(64,245)		(7,398)	(60,860)		(19,078)
Other income (expense), net		(26,457)		5,878	(34,972)		1,276
Income (loss) from continuing operations before provision (benefit) for income taxes		(90,702)		(1,520)	(95,832)		(17,802)
Provision (benefit) for income taxes		1,552		3,883	(783)		8,470
Income (loss) from continuing operations		(92,254)		(5,403)	(95,049)		(26,272)
Income (loss) from discontinued operations, net of tax		0		(1,376)	0		(889)
Net income (loss)		(92,254)		(6,779)	(95,049)		(27,161)
Net income attributable to noncontrolling interests		(2,780)		(2,547)	(6,873)		(6,579)
Net income (loss) attributable to Groupon, Inc.		$ (95,034)		$ (9,326)	$ (101,922)		$ (33,740)
Basic and diluted net income (loss) per share:
Continuing operations (in usd per share)		$ (0.17)		$ (0.01)	$ (0.18)		$ (0.06)
Discontinued operations (in usd per share)		0		(0.01)	0		0
Basic and diluted net income (loss) per share (in usd per share)		$ (0.17)		$ (0.02)	$ (0.18)		$ (0.06)
Weighted average number of shares outstanding
Basic (in shares)		565,284,705		559,762,180	563,502,954		560,978,712
Diluted (in shares)		565,284,705		559,762,180	563,502,954		560,978,712
[1]	(1)For the three months ended June 30, 2018, reflects a $9.2 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, and an increase of $0.5 million related to the timing of recognition of revenue from hotel reservation offerings, partially offset by decreases of $2.9 million related to the timing of recognition of variable consideration from unredeemed vouchers and $0.8 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used.
[2]	(1)North America includes revenue from the United States of $371.1 million and $442.7 million for the three months ended June 30, 2018 and 2017, respectively, and $756.5 million and $907.4 million for the six months ended June 30, 2018 and 2017, respectively. International includes revenue from the United Kingdom of $91.5 million and $74.4 million for the three months ended June 30, 2018 and 2017, respectively, and $174.5 million and $139.9 million for the six months ended June 30, 2018 and 2017, respectively. There were no other individual countries that represented more than 10% of consolidated total revenue for the three and six months ended June 30, 2018 and 2017.
[3]	Reflects an increase for refunds on service revenue transactions for which the merchant's share is not recoverable, which are classified as a reduction of revenue under Topic 606.
[4]	Reflects an increase for customer credits issued for relationship purposes, which are classified as a reduction of revenue under Topic 606.
[5]	Reflects the amortization of deferred contract acquisition costs in excess of amounts capitalized in the current period.
[6]	(1)Includes stock-based compensation of $15.0 million and $20.0 million for North America and $1.3 million and $1.3 million for International for the three months ended June 30, 2018 and 2017, respectively, and
[7]	Includes restructuring charges (credits) of $0.2 million and $3.0 million for North America and $(0.6) million and $1.6 million for International for the three months ended June 30, 2018 and 2017, respectively

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Statement of Income Captions [Line Items]
Income (loss) from continuing operations	$ (92,254)	$ (5,403)	$ (95,049)	$ (26,272)
Other comprehensive income (loss) from continuing operations:
Net change in unrealized gain (loss) on foreign currency translation adjustments			1,238
Net change in unrealized gain (loss) on defined benefit pension plan	0	0	0	585
Net unrealized gain (loss) during the period	(541)	(952)	(1,042)	(713)
Reclassification adjustment for realized (gain) loss on investment included in income (loss) from continuing operations	106	(1,341)	106	(1,341)
Net change in unrealized gain (loss) on available-for-sale securities (net of tax effect of $0 and $147 for the three months ended June 30, 2018 and 2017, respectively, and $0 and $0 for the six months ended June 30, 2018 and 2017, respectively)	(435)	(2,293)	(936)	(2,054)
Income (loss) from discontinued operations	0	(1,376)	0	(889)
Other comprehensive income (loss) from discontinued operations - Foreign currency translation adjustments:
Other comprehensive income (loss)	2,371	(8,437)	302	(7,183)
Comprehensive income (loss)	(89,883)	(15,216)	(94,747)	(50,855)
Comprehensive income (loss) attributable to noncontrolling interests	(2,780)	(2,547)	(6,873)	(6,579)
Comprehensive income (loss) attributable to Groupon, Inc.	(92,663)	(17,763)	(101,620)	(57,434)
Tax effect	0	147	0	0
Continuing Operations
Other comprehensive income (loss) from continuing operations:
Net change in unrealized gain (loss) on foreign currency translation adjustments	2,806	(6,144)	1,238	(5,714)
Other comprehensive income (loss) from discontinued operations - Foreign currency translation adjustments:
Comprehensive income (loss)	(89,883)	(13,840)	(94,747)	(33,455)
Discontinued Operations, Disposed of by Sale
Other comprehensive income (loss) from continuing operations:
Net change in unrealized gain (loss) on foreign currency translation adjustments	0	0	0	(16,511)
Other comprehensive income (loss) from discontinued operations - Foreign currency translation adjustments:
Net unrealized gain (loss) during the period	0	0	0	(1,793)
Reclassification adjustment included in net income (loss) from discontinued operations	0	0	0	(14,718)
Other comprehensive income (loss)	$ 0	$ (1,376)	$ 0	$ (17,400)

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total Groupon, Inc. Stockholders' Equity	Non-controlling Interests
Beginning balance (in shares) at Dec. 31, 2017		748,541,862
Beginning balance at Dec. 31, 2017	$ 251,845	$ 75	$ 2,174,708		$ (1,088,204)	$ 31,844	$ 250,973	$ 872
Treasury stock, beginning balance (in shares) at Dec. 31, 2017				(188,602,242)
Treasury stock, beginning balance at Dec. 31, 2017	867,450			$ (867,450)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle, net of tax	88,945				88,945		88,945
Reclassification for impact of U.S. tax rate change					(161)	161
Net income (loss) attributable to noncontrolling interest	(95,049)				(101,922)			6,873
Net income (loss) attributable to parent	(101,922)						(101,922)
Foreign currency translation	1,238					1,238	1,238
Unrealized gain (loss) on available-for-sale securities, net of tax	$ (936)					(936)	(936)
Exercise in stock options (in shares)	667,743	667,743
Exercise of stock options	$ 70		70				70
Vesting of restricted stock units and performance share units (in shares)		7,785,719
Vesting of restricted stock units and performance share units		$ 1	(1)
Shares issued under employee stock purchase plan (in shares)		746,773
Shares issued under employee stock purchase plan	2,434		2,434				2,434
Shares issued to settle liability-classified awards (in shares)		1,240,379
Shares issued to settle liability-classified awards	6,436		6,436				6,436
Tax withholdings related to net share settlements of stock-based compensation awards (in shares)		(3,175,849)
Tax withholdings related to net share settlements of stock-based compensation awards	(14,499)		(14,499)				(14,499)
Stock-based compensation on equity-classified awards	37,593		37,593				37,593
Distributions to noncontrolling interest holders	(6,940)							(6,940)
Ending balance (in shares) at Jun. 30, 2018		755,806,627
Ending balance at Jun. 30, 2018	271,137	$ 76	$ 2,206,741		$ (1,101,342)	$ 32,307	$ 270,332	$ 805
Treasury stock, ending balance (in shares) at Jun. 30, 2018				(188,602,242)
Treasury stock, ending balance at Jun. 30, 2018	$ 867,450			$ (867,450)

CONDENSED CONSOLIDATED STATEME7

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net income (loss)	$ (95,049)	$ (27,161)
Less: Income (loss) from discontinued operations, net of tax	0	889
Income (loss) from continuing operations	(95,049)	(26,272)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization of property, equipment and software	52,149	57,163
Amortization of acquired intangible assets	6,466	11,583
Stock-based compensation	35,644	41,141
Impairments of Investments	10,044	0
Deferred income taxes	(6,575)	759
(Gain) loss from changes in fair value of investments	8,068	1,145
Amortization of debt discount on convertible senior notes	5,806	5,242
Change in assets and liabilities, net of acquisitions and dispositions:
Accounts receivable	27,296	16,229
Prepaid expenses and other current assets	1,489	(11,139)
Accounts payable	(9,340)	(10,723)
Accrued merchant and supplier payables	(172,982)	(182,954)
Accrued expenses and other current liabilities	51,140	(41,491)
Other, net	10,272	(18,159)
Net cash provided by (used in) operating activities from continuing operations	(75,572)	(157,476)
Net cash provided by (used in) operating activities from discontinued operations	0	(2,195)
Net cash provided by (used in) operating activities	(75,572)	(159,671)
Investing activities
Purchases of property and equipment and capitalized software	(37,517)	(29,461)
Proceeds from maturity of investment	0	1,843
Acquisition of business, net of acquired cash	(57,821)	0
Acquisitions of intangible assets and other investing activities	(758)	(184)
Net cash provided by (used in) investing activities from continuing operations	(96,096)	(27,802)
Net cash provided by (used in) investing activities from discontinued operations	0	(9,548)
Net cash provided by (used in) investing activities	(96,096)	(37,350)
Financing activities
Payments for purchases of treasury stock	0	(51,513)
Taxes paid related to net share settlements of stock-based compensation awards	(16,138)	(15,356)
Proceeds from stock option exercises and employee stock purchase plan	2,504	2,477
Distributions to noncontrolling interest holders	(6,940)	(6,426)
Payments of capital lease obligations	(17,239)	(16,670)
Payments of contingent consideration related to acquisitions	(1,815)	(5,689)
Other financing activities	0	(473)
Net cash provided by (used in) financing activities	(39,628)	(93,650)
Effect of exchange rate changes on cash, cash equivalents and restricted cash, including cash classified within current assets of discontinued operations	(6,644)	17,297
Net increase (decrease) in cash, cash equivalents and restricted cash, including cash classified within current assets of discontinued operations	(217,940)	(273,374)
Less: Net increase (decrease) in cash classified within current assets of discontinued operations	0	(28,866)
Net increase (decrease) in cash, cash equivalents and restricted cash	(217,940)	(244,508)
Cash, cash equivalents and restricted cash, beginning of period	885,481	874,906
Cash, cash equivalents and restricted cash, end of period	667,541	630,398
Non-cash investing and financing activities
Equipment acquired under capital lease obligations	9,581	16,509
Leasehold improvements funded by lessor	557	402
Liability for purchases of treasury stock	0	561
Increase (decrease) in liabilities related to purchases of property and equipment and capitalized software	(789)	(539)
Investments acquired in connection with business dispositions	0	2,022
Contingent consideration liability incurred in connection with acquisition of business	1,589	0
Financing obligation incurred in connection with acquisition of business	$ 8,604	$ 0

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Company Information Groupon, Inc. and subsidiaries (the "Company"), which commenced operations in October 2008, operates online local commerce marketplaces throughout the world that connect merchants to consumers by offering goods and services, generally at a discount. Customers access those marketplaces through the Company's websites, primarily localized groupon.com sites in many countries, and its mobile applications. The Company's operations are organized into two segments: North America and International. See Note 16 , Segment Information . Unaudited Interim Financial Information The Company has prepared the accompanying condensed consolidated financial statements pursuant to the rules and regulations of the Securities and Exchange Commission ("SEC") for interim financial reporting. These condensed consolidated financial statements are unaudited and, in the Company's opinion, include all adjustments, consisting of normal recurring adjustments and accruals, necessary for a fair presentation of the Company's condensed consolidated balance sheets, statements of operations, comprehensive income (loss), cash flows and stockholders' equity for the periods presented. Operating results for the periods presented are not necessarily indicative of the results to be expected for the full year ending December 31, 2018 . Certain information and disclosures normally included in financial statements prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP") have been omitted in accordance with the rules and regulations of the SEC. These condensed consolidated financial statements and notes should be read in conjunction with the audited consolidated financial statements and notes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 , filed with the SEC on February 14, 2018, as amended by the Form 10-K/A for the year ended December 31, 2017, filed with the SEC on March 23, 2018. Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. The Company's condensed consolidated financial statements were prepared in accordance with U.S. GAAP and include the assets, liabilities, revenue and expenses of all wholly-owned subsidiaries and majority-owned subsidiaries over which the Company exercises control and variable interest entities for which the Company has determined that it is the primary beneficiary. Outside stockholders' interests in subsidiaries are shown on the condensed consolidated financial statements as Noncontrolling interests. Equity investments in entities in which the Company does not have a controlling financial interest are accounted for under the equity method, the fair value option, as available-for-sale securities or at cost adjusted for observable price changes and impairments, as appropriate. Reclassifications and Terminology Changes Certain reclassifications have been made to the condensed consolidated financial statements of prior periods and the accompanying notes to conform to the current period presentation, including the change in presentation of restricted cash in the condensed consolidated statements of cash flows upon adoption of ASU 2016-18. Refer to Note 2 , Adoption of New Accounting Standards , for additional information. Additionally, in prior years, the Company referred to its product revenue and service revenue as "direct revenue" and "third-party and other revenue," respectively. This terminology change did not impact the amounts presented in the condensed consolidated financial statements. Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires estimates and assumptions that affect the reported amounts and classifications of assets and liabilities, revenue and expenses, and the related disclosures of contingent liabilities in the condensed consolidated financial statements and accompanying notes. Estimates are used for, but not limited to, variable consideration from unredeemed vouchers, income taxes, valuation of goodwill and intangible assets, investments, customer refunds, contingent liabilities and the useful lives of property, equipment and software and intangible assets. Actual results could differ materially from those estimates.

ADOPTION OF NEW ACCOUNTING STAN

ADOPTION OF NEW ACCOUNTING STANDARDS	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
ADOPTION OF NEW ACCOUNTING STANDARDS	ADOPTION OF NEW ACCOUNTING STANDARDS The Company adopted the guidance in ASC Topic 606, Revenue from Contracts with Customers , on January 1, 2018. Topic 606 is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods or services. See Changes to Accounting Policies from Adoption of New Accounting Standards below and Note 11 , Revenue Recognition , for information on the impact of adopting Topic 606 on the Company's accounting policies. The Company adopted the guidance in ASU 2016-01, Financial Instruments (Topic 825-10) - Recognition and Measurement of Financial Assets and Financial Liabilities , as amended, on January 1, 2018 . This ASU generally requires equity investments to be measured at fair value with changes in fair value recognized through net income and eliminates the cost method for equity securities. However, for equity investments without readily determinable fair values the ASU permits entities to elect to measure the investments at cost adjusted for observable price changes and impairments, with changes in the measurement recognized through net income. The Company applied that measurement alternative to our equity investments that were previously accounted for under the cost method. The adoption of ASU 2016-01 did not have a material impact on the condensed consolidated financial statements. See Changes to Accounting Policies from Adoption of New Accounting Standards below for additional information on the impact of adopting the ASU on the Company's accounting policies. The Company adopted the guidance in ASU 2016-18, Statement of Cash Flows (Topic 230) - Restricted Cash , on January 1, 2018. This ASU requires companies to include amounts generally described as restricted cash and restricted cash equivalents, along with cash and cash equivalents, when reconciling the beginning-of-period and end-of-period amounts shown on the statement of cash flows. Previously, changes in restricted cash were reported within cash flows from operating activities. The Company applied that change in cash flow classification on a retrospective basis, which resulted in an increase of $0.5 million to net cash used in operating activities for the six months ended June 30, 2017 . Restricted cash primarily represents amounts that the Company is unable to access for operational purposes pursuant to letters of credit with financial institutions. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets to amounts shown in the condensed consolidated statements of cash flows, as of June 30, 2018 and 2017 and December 31, 2017 (in thousands): June 30, 2018 June 30, 2017 December 31, 2017 Cash and cash equivalents $ 662,893 $ 618,550 $ 880,129 Restricted cash included in prepaid expenses and other current assets 4,250 6,569 4,932 Restricted cash included in other non-current assets 398 5,279 420 Cash, cash equivalents and restricted cash $ 667,541 $ 630,398 $ 885,481 The Company adopted the guidance in ASU 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20) - Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets , on January 1, 2018. This ASU is meant to clarify the scope of ASC Subtopic 610-20, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets , and to add guidance for partial sales of nonfinancial assets. The adoption of ASU 2017-05 did not have a material impact on the condensed consolidated financial statements. The Company adopted the guidance in ASU 2017-07, Compensation - Retirement Benefits (Topic 715) - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost , on January 1, 2018. This ASU requires employers to include only the service cost component of net periodic pension cost in operating expenses, together with other employee compensation costs. The other components of net periodic pension cost, including interest cost, expected return on plan assets, amortization of prior service cost and settlement and curtailment effects, are to be included in non-operating expenses. The adoption of ASU 2017-07 did not have a material impact on the condensed consolidated financial statements. The Company adopted the guidance in ASU 2017-09, Compensation - Stock Compensation (Topic 718) - Scope of Modification Accounting , on January 1, 2018. This ASU clarifies the changes to terms or conditions of a share-based payment award that require an entity to apply modification accounting. The adoption of ASU 2017-09 did not have a material impact on the condensed consolidated financial statements. The Company adopted the guidance in ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, as of January 1, 2018. This ASU permits a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act (the "Jobs Act"). As a result of the adoption of ASU 2018-02, the Company reclassified $0.2 million from accumulated other comprehensive income (loss) to accumulated deficit. Changes to Accounting Policies from Adoption of New Accounting Standards Revenue Recognition Prior to its adoption of Topic 606, the Company recognized revenue when the following criteria were met: persuasive evidence of an arrangement existed; delivery had occurred; the selling price was fixed or determinable and collection was reasonably assured. Following its adoption of Topic 606, the Company recognizes revenue when it satisfies a performance obligation by transferring a promised good or service to a customer. Substantially all of the Company's performance obligations are satisfied at a point in time rather than over time. Product Revenue The Company generates product revenue from direct sales of merchandise inventory through its Goods category. For product revenue transactions, the Company is the primary party responsible for providing the good to the customer, it has inventory risk and it has discretion in establishing prices. As such, product revenue is reported on a gross basis as the purchase price received from the customer. Product revenue, including associated shipping revenue, is recognized when title passes to the customer upon delivery of the product. Service Revenue Service revenue is primarily earned from transactions in which the Company earns commissions by selling goods or services on behalf of third-party merchants. Those transactions generally involve a customer's purchase of a voucher through one of the Company's online marketplaces that can be redeemed with a third-party merchant for specified goods or services (or for discounts on specified goods or services). Service revenue from those transactions is reported on a net basis as the purchase price collected from the customer less the portion of the purchase price that is payable to the third-party merchant. The Company recognizes revenue from those transactions when its commission has been earned, which occurs when a sale through one of the Company's online marketplaces is completed and the related voucher has been made available to the customer. The Company believes that its remaining obligations to remit payment to the merchant and to provide information about vouchers sold are administrative activities that are immaterial in the context of the contract with the merchant. Prior to its adoption of Topic 606, the Company deferred the revenue from hotel reservation offerings until the customer's stay commenced. Following its adoption of Topic 606, revenue from hotel reservation offerings is recognized at the time the reservation is made, net of an allowance for estimated cancellations. The Company also earns commissions when customers make purchases with retailers using digital coupons accessed through its websites and mobile applications and from voucherless merchant offerings in which customers earn cash back on their credit card statements when they transact with third-party merchants. The Company recognizes those commissions as revenue in the period in which the underlying transactions between the customer and the third-party merchant are completed. Variable Consideration for Unredeemed Vouchers For merchant agreements with redemption payment terms, the merchant is not paid its share of the sale price for a voucher sold through one of the Company's online marketplaces until the customer redeems the related voucher. If the customer does not redeem a voucher with such merchant payment terms, the Company retains all of the gross billings for that voucher, rather than retaining only its net commission. Prior to its adoption of Topic 606, the Company recognized that variable consideration from unredeemed vouchers and derecognized the related accrued merchant payables when its legal obligation to the merchant expired, which the Company believes is shortly after the voucher expiration date in most jurisdictions. Following its adoption of Topic 606, the Company estimates the variable consideration from vouchers that will not ultimately be redeemed and recognizes that amount as revenue at the time of sale, rather than when the Company's legal obligation expires. The Company estimates variable consideration from unredeemed vouchers using its historical voucher redemption experience. If actual redemptions differ from the Company's estimates, the effects could be material to the condensed consolidated financial statements. Refunds Prior to the adoption of Topic 606, refunds were recorded as a reduction of revenue, except for refunds on service revenue transactions for which the merchant's share was not recoverable, which were presented as a cost of revenue. Following the adoption of Topic 606, all refunds are recorded as a reduction of revenue. The liability for estimated refunds is included within Accrued expenses and other current liabilities on the condensed consolidated balance sheets. The Company estimates its refund reserve using historical refund experience by deal category. The Company assesses the trends that could affect its estimates on an ongoing basis and makes adjustments to the refund reserve calculations if it appears that changes in circumstances, including changes to the Company's refund policies or general economic conditions, may cause future refunds to differ from its initial estimates. If actual refunds differ from the Company's estimates, the effects could be material to the condensed consolidated financial statements. Discounts, Customer Credits and Other Consideration Payable to Customers The Company provides discount offers to encourage purchases of goods and services through its online marketplaces. The Company records discounts as a reduction of revenue. Additionally, the Company issues credits to customers that can be applied to future purchases through its online marketplaces. Credits are primarily issued as consideration for refunds. To a lesser extent, credits are issued for customer relationship purposes. Credits issued to satisfy refund requests are applied as a reduction to the refunds reserve. Prior to the adoption of Topic 606, customer credits issued for relationship purposes were classified in the condensed consolidated statement of operations as a marketing expense. Following the adoption of Topic 606, customer credits issued for relationship purposes are classified as a reduction of revenue. Prior to its adoption of Topic 606, the Company recognized breakage income for unused customer credits when they expired or were forfeited. Following its adoption of Topic 606, breakage income from customer credits that are not expected to be used is estimated and recognized as revenue in proportion to the pattern of redemption for customer credits that are used. Sales and Related Taxes Sales, use, value-added and related taxes that are imposed on specific revenue-generating transactions are presented on a net basis and excluded from revenue. Costs of Obtaining Contracts Prior to its adoption of Topic 606, the Company expensed the incremental costs to obtain contracts with third-party merchants, such as sales commissions, as incurred. Following its adoption of Topic 606, those costs are deferred and recognized over the expected period of the merchant arrangement, generally from 12 to 18 months. As of June 30, 2018 , the Company had $3.4 million and $11.5 million of deferred contract acquisition costs recorded within Prepaid expenses and other current assets and Other non-current assets, respectively. For the three and six months ended June 30, 2018 , the Company amortized $6.5 million and $13.3 million , respectively, of deferred contract acquisition costs and did not recognize any impairment losses in relation to the deferred costs. Those costs are classified within Selling, general and administrative expenses in the condensed consolidated statements of operations. Cost of Revenue Cost of revenue is comprised of direct and certain indirect costs incurred to generate revenue. Costs incurred to generate revenue, which include credit card processing fees, editorial costs, compensation expense for technology support personnel who are responsible for maintaining the infrastructure of the Company's websites, amortization of internal-use software relating to customer-facing applications, web hosting and other processing fees are attributed to the cost of service and product revenue in proportion to gross billings during the period. For product revenue transactions, cost of revenue also includes the cost of inventory, shipping and fulfillment costs and inventory markdowns. Fulfillment costs are comprised of third-party logistics provider costs, as well as rent, depreciation, personnel costs and other costs of operating the Company's fulfillment center. Prior to adoption of Topic 606, cost of revenue on service revenue transactions also included refunds for which the merchant's share was not recoverable. Investments Prior to the adoption of the guidance in ASU 2016-01, investments in nonmarketable equity shares with no redemption provisions that are not common stock or in-substance common stock or for which the Company does not have the ability to exercise significant influence were accounted for using the cost method of accounting. Those investments are classified within Investments on the condensed consolidated balance sheets. Under the cost method of accounting, investments were carried at cost and adjusted only for other-than-temporary declines in fair value, certain distributions and additional investments. Subsequent to the adoption of the guidance in ASU 2016-01, the Company applies a measurement alternative for equity investments without readily determinable fair values that permits entities to elect to measure the investments at cost adjusted for observable price changes and impairments, with changes in the measurement recognized through net income. Investments in common stock or in-substance common stock for which the Company has the ability to exercise significant influence are accounted for under the equity method, except where the Company has made an irrevocable election to account for the investments at fair value. Those investments are classified within Investments on the condensed consolidated balance sheets. The Company's proportionate share of income or loss on equity method investments and changes in the fair values of investments for which the fair value option has been elected are presented within Other income (expense), net on the condensed consolidated statements of operations. Investments in convertible debt securities and convertible redeemable preferred shares are accounted for as available-for-sale securities, which are classified within Prepaid expenses and other current assets and Investments on the condensed consolidated balance sheets. Available-for-sale securities are recorded at fair value each reporting period. Unrealized gains and losses, net of the related tax effects, are excluded from earnings and recorded as a separate component within Accumulated other comprehensive income (loss) on the condensed consolidated balance sheets until realized. Interest income from available-for-sale securities is reported within Other income (expense), net on the condensed consolidated statements of operations.

DISCONTINUED OPERATIONS AND OTH

DISCONTINUED OPERATIONS AND OTHER BUSINESS DISPOSITIONS	6 Months Ended
	Jun. 30, 2018
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax [Abstract]
DISCONTINUED OPERATIONS AND OTHER BUSINESS DISPOSITIONS	DISCONTINUED OPERATIONS AND OTHER BUSINESS DISPOSITIONS In October 2016, the Company completed a strategic review of its international markets in connection with its efforts to optimize its global footprint and focus on the markets that it believes have the greatest potential to benefit the Company's long-term financial performance. Based on that review, the Company decided to focus its business on 15 core countries and to pursue strategic alternatives for its operations in the remaining 11 countries, which were primarily based in Asia and Latin America. The dispositions of the Company's operations in those 11 countries were completed between November 2016 and March 2017. A business disposition that represents a strategic shift and has (or will have) a major effect on an entity's operations and financial results is reported as a discontinued operation. The Company determined that the decision reached by its management and Board of Directors to exit those 11 non-core countries, which comprised a substantial majority of its operations outside of North America and EMEA, represented a strategic shift in its business. Additionally, based on its review of quantitative and qualitative factors relevant to the dispositions, the Company determined that the disposition of the businesses in those countries would have a major effect on its operations and financial results. As such, the results of operations and cash flows for its operations in those countries, including the gains and losses on the dispositions and related income tax effects, are presented as discontinued operations in the accompanying condensed consolidated financial statements for the three and six months ended June 30, 2018 and 2017 . Dispositions Completed in 2017 In connection with its strategic initiative to exit non-core countries as discussed above, the Company sold an 83% controlling stake in its subsidiary in Israel and sold its subsidiaries in Argentina, Chile, Colombia, Peru, Mexico, Brazil, Singapore and Hong Kong during the first quarter 2017. The Company recognized a net pretax loss on those dispositions of $1.3 million , which consisted of the following (in thousands): Net consideration received: Fair value of minority investments retained or acquired $ 2,021 Cash proceeds received 3,462 Cash proceeds receivable 2,000 Less: transaction costs 1,394 Total net consideration received 6,089 Cumulative translation gain reclassified to earnings 14,718 Less: Net book value upon closing of the transactions 14,596 Less: Indemnification liabilities (1) 5,365 Less: Unfavorable contract liability for transition services 2,114 Loss on dispositions $ (1,268 ) (1) See Note 9 , Commitments and Contingencies , for additional information about the indemnification liabilities. Results of Discontinued Operations The following table summarizes the major classes of line items included in income (loss) from discontinued operations, net of tax, for the three and six months ended June 30, 2017 (in thousands): Three Months Ended June 30, 2017 (1) Six Months Ended June 30, 2017 (2) Service revenue $ — $ 12,602 Product revenue — 2,962 Service cost of revenue — (2,557 ) Product cost of revenue — (3,098 ) Marketing expense — (1,239 ) Selling, general and administrative expense (1,376 ) (11,284 ) Restructuring — (778 ) Other income, net — 3,852 Income (loss) from discontinued operations before loss on dispositions and provision for income taxes (1,376 ) 460 Loss on dispositions — (1,268 ) Provision for income taxes — (81 ) Income (loss) from discontinued operations, net of tax $ (1,376 ) $ (889 ) (1) Selling, general and administrative expenses from discontinued operations for the three months ended June 30, 2017 primarily related to increases to contingent liabilities under indemnification agreements. See Note 9, Commitments and Contingencies , for information about indemnification obligations related to discontinued operations. (2) The income (loss) from discontinued operations before loss on dispositions and provision for income taxes for the six months ended June 30, 2017 includes the results of each business through its respective disposition date.

BUSINESS COMBINATIONS

BUSINESS COMBINATIONS	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
BUSINESS COMBINATIONS	BUSINESS COMBINATIONS On April 30, 2018, the Company acquired 80% of the outstanding shares of Cloud Savings Company, Ltd. ("Cloud Savings"), a UK-based business that operates online discount code and digital gift card platforms. The primary purpose of this acquisition was to expand digital coupon offerings in the Company's international segment. Concurrent with the acquisition, the Company entered into an agreement with the noncontrolling shareholder giving the Company the right to acquire the remaining outstanding shares of Cloud Savings for $8.9 million in December 2018. Additionally, the noncontrolling shareholder has the right to require the Company to purchase its shares in December 2018 for that same amount. The rights and obligations to acquire the remaining outstanding shares were recorded as a financing obligation at its acquisition-date fair value of $8.6 million and is classified within Accrued expenses and other current liabilities on the condensed consolidated balance sheets. The transaction also included a contingent consideration arrangement with an acquisition-date fair value of $1.6 million . The aggregate acquisition-date fair value of the consideration transferred for the Cloud Savings acquisition totaled $74.3 million , which consisted of the following (in thousands): Cash $ 64,065 Financing obligation 8,604 Contingent consideration 1,589 Total $ 74,258 The results of the Cloud Savings acquisition are included in the condensed consolidated financial statements from the date of acquisition through June 30, 2018. The fair value of consideration transferred in the business combination is allocated to the tangible and intangible assets acquired and liabilities assumed at the acquisition date, with the remaining unallocated amount recorded as goodwill. Acquired goodwill represents the premium the Company paid over the fair value of the net tangible and intangible assets acquired. The Company paid a premium for a number of reasons, including growing the Company's merchant base and acquiring an assembled workforce. The goodwill from this business combination is not deductible for tax purposes. The allocation of the acquisition price has been prepared on a preliminary basis, and changes to that allocation may occur as a result of final working capital adjustments and tax return filings. The following table summarizes the allocation of the aggregate acquisition price of the Cloud Savings acquisition (in thousands): Cash and cash equivalents $ 6,244 Accounts receivable 5,885 Prepaid expenses and other current assets 804 Property, equipment and software 226 Goodwill 46,217 Intangible assets (1) : Merchant relationships 20,322 Trade names 2,609 Developed technology 549 Other intangible assets 687 Total assets acquired $ 83,543 Accounts payable $ 693 Accrued merchant and supplier payables 386 Accrued expenses and other current liabilities 6,130 Other non-current liabilities 2,076 Total liabilities assumed $ 9,285 Total acquisition price $ 74,258 (1) The estimated useful lives of the acquired intangible assets are 6 years for merchant relationships, 8 years for trade names, 2 years for developed technology, and 1 year for other intangible assets. For the three and six months ended June 30, 2018 , $0.7 million of external transaction costs related to that business combination, primarily consisting of legal and advisory fees, are classified within Selling, general and administrative on the condensed consolidated statements of operations. The revenue and net loss of Cloud Savings included in the Company's condensed consolidated statements of operations were $3.0 million and $0.1 million , respectively, for the period from April 30, 2018 through June 30, 2018. Pro forma results of operations for the Cloud Savings acquisition are not presented as the pro forma effects of that acquisition were not material to the Company's condensed consolidated results of operations.

GOODWILL AND OTHER INTANGIBLE A

GOODWILL AND OTHER INTANGIBLE ASSETS	6 Months Ended
	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND OTHER INTANGIBLE ASSETS	GOODWILL AND OTHER INTANGIBLE ASSETS The following table summarizes the Company's goodwill activity by segment for the six months ended June 30, 2018 (in thousands): North America International Consolidated Balance as of December 31, 2017 $ 178,685 $ 108,304 $ 286,989 Goodwill related to acquisition — 46,217 46,217 Foreign currency translation — (4,407 ) (4,407 ) Balance as of June 30, 2018 $ 178,685 $ 150,114 $ 328,799 The following table summarizes the Company's intangible assets as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Asset Category Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Customer relationships $ 55,952 $ 48,695 $ 7,257 $ 56,749 $ 46,513 $ 10,236 Merchant relationships 30,969 10,778 20,191 11,598 9,853 1,745 Trade names 14,456 10,965 3,491 12,077 10,469 1,608 Developed technology 37,151 36,667 484 36,864 36,864 — Patents 20,132 15,895 4,237 19,031 15,204 3,827 Other intangible assets 11,342 9,927 1,415 10,875 9,095 1,780 Total $ 170,002 $ 132,927 $ 37,075 $ 147,194 $ 127,998 $ 19,196 Amortization of intangible assets is computed using the straight-line method over their estimated useful lives, which range from 1 to 8 years. Amortization expense related to intangible assets was $3.5 million and $6.2 million for the three months ended June 30, 2018 and 2017 , respectively, and $6.4 million and $11.6 million for the six months ended June 30, 2018 and 2017 , respectively. As of June 30, 2018 , the Company's estimated future amortization expense related to intangible assets is as follows (in thousands): Remaining amounts in 2018 $ 7,446 2019 11,025 2020 5,120 2021 4,393 2022 4,077 Thereafter 5,014 Total $ 37,075

INVESTMENTS

INVESTMENTS	6 Months Ended
	Jun. 30, 2018
Schedule of Equity Method Investments [Abstract]
INVESTMENTS	INVESTMENTS The following table summarizes the Company's investments as of June 30, 2018 and December 31, 2017 (dollars in thousands): June 30, 2018 Percent Ownership of Voting Stock December 31, 2017 Percent Ownership of Voting Stock Current (1) : Available-for-sale securities: Convertible debt securities $ 8,517 $ — Non-current (1) : Available-for-sale securities: Convertible debt securities $ 1,719 $ 11,354 Redeemable preferred shares 9,961 19% to 25% 15,431 19% to 25% Total available-for-sale securities 11,680 26,785 Fair value option investments 74,898 10% to 19% 82,966 10% to 19% Other equity investments (2) 23,028 1% to 19% 25,438 1% to 19% Total non-current investments $ 109,606 $ 135,189 Total investments $ 118,123 $ 135,189 (1) Current and non-current investments are classified within Prepaid expenses and other current assets and Investments, respectively, on the condensed consolidated balance sheets. (2) Represents equity investments without readily determinable fair values. Those investments were previously accounted for using the cost method of accounting. Under the cost method, investments were carried at cost and adjusted only for other-than-temporary declines in fair value, certain distributions and additional investments. The Company adopted the guidance in ASU 2016-01 on January 1, 2018. Under that guidance, the Company has elected to record equity investments without readily determinable fair values at cost adjusted for observable price changes and impairments. There were no adjustments for observable price changes related to these investments for the three and six months ended June 30, 2018 . See further discussion under Impairments of Investments below. The following table summarizes the amortized cost, gross unrealized gain, gross unrealized loss and fair value of the Company's available-for-sale securities as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Amortized Cost Gross Unrealized Gain Gross Unrealized Loss (1) Fair Value Available-for-sale securities: Convertible debt securities $ 10,129 $ 107 $ — $ 10,236 $ 10,205 $ 1,653 $ (504 ) $ 11,354 Redeemable preferred shares 9,961 — — 9,961 15,431 — — 15,431 Total available-for-sale securities $ 20,090 $ 107 $ — $ 20,197 $ 25,636 $ 1,653 $ (504 ) $ 26,785 (1) Gross unrealized loss is related to one security that was in a loss position for greater than 12 months as of December 31, 2017. Fair Value Option Investments In connection with the dispositions of controlling stakes in Ticket Monster, an entity based in the Republic of Korea, in May 2015 and Groupon India in August 2015, the Company obtained minority investments in Monster Holdings LP ("Monster LP") and in Nearbuy Pte Ltd. ("Nearbuy"), respectively. The Company has made an irrevocable election to account for both of those investments at fair value with changes in fair value reported in earnings. The Company elected to apply fair value accounting to those investments because it believes that fair value is the most relevant measurement attribute for those investments, as well as to reduce operational and accounting complexity. The Company determined that the fair value of its investments in Monster LP and Nearbuy were $70.6 million and $4.3 million , respectively, as of June 30, 2018 and $78.9 million and $4.0 million , respectively, as of December 31, 2017 . The following table summarizes the Company’s gains and losses due to changes in fair value of those investments for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Monster LP $ (3,054 ) $ (77 ) $ (8,285 ) $ 2,276 Nearbuy 19 (1,371 ) 217 (3,421 ) Total $ (3,035 ) $ (1,448 ) $ (8,068 ) $ (1,145 ) Impairments of Investments The Company recorded other-than-temporary impairments of available-for-sale securities of $4.6 million and $5.4 million for the three and six months ended June 30, 2018 , respectively. The Company also recorded a $4.6 million impairment of an other equity investment for the three and six months ended June 30, 2018 . Those impairments are classified within Other income (expense), net on the condensed consolidated statements of operations.

SUPPLEMENTAL CONSOLIDATED BALAN

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION	6 Months Ended
	Jun. 30, 2018
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION	SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION The following table summarizes the Company's other income (expense), net for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Interest income $ 1,836 $ 659 $ 3,345 $ 1,261 Interest expense (5,228 ) (4,948 ) (10,721 ) (10,267 ) Gains (losses), net on changes in fair value of investments (3,035 ) (1,448 ) (8,068 ) (1,145 ) Foreign currency gains (losses), net (12,533 ) 10,826 (11,135 ) 10,877 Impairments of investments (9,189 ) — (10,044 ) — Other 1,692 789 1,651 550 Other income (expense), net $ (26,457 ) $ 5,878 $ (34,972 ) $ 1,276 The following table summarizes the Company's prepaid expenses and other current assets as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Merchandise inventories $ 28,307 $ 25,528 Prepaid expenses 38,519 40,399 Income taxes receivable 9,565 10,299 Investments 8,517 — Other 19,616 17,799 Total prepaid expenses and other current assets $ 104,524 $ 94,025 The following table summarizes the Company's accrued merchant and supplier payables as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Accrued merchant payables $ 377,097 $ 459,662 Accrued supplier payables (1) 151,127 310,673 Total accrued merchant and supplier payables $ 528,224 $ 770,335 (1) Amounts include payables to suppliers of inventories and providers of shipping and fulfillment services. The following table summarizes the Company's accrued expenses and other current liabilities as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Refunds reserve $ 30,355 $ 31,275 Compensation and benefits 55,827 73,096 Accrued marketing 29,297 32,912 Customer credits 18,316 28,487 Income taxes payable 12,448 9,645 Deferred revenue 21,802 29,539 Current portion of capital lease obligations 23,808 25,958 Accrued litigation and other (1) 175,666 100,284 Total accrued expenses and other current liabilities $ 367,519 $ 331,196 (1) Includes an $82.5 million accrual as of June 30, 2018 related to IBM patent litigation. See Note 9 , Commitments and Contingencies, for additional information. The following table summarizes the Company's other non-current liabilities as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Contingent income tax liabilities $ 45,326 $ 43,699 Deferred rent 31,434 29,032 Capital lease obligations 12,990 18,500 Deferred income taxes 2,841 811 Other 10,644 10,366 Total other non-current liabilities $ 103,235 $ 102,408 The following table summarizes the components of accumulated other comprehensive income (loss) as of June 30, 2018 and December 31, 2017 (in thousands): Foreign currency translation adjustments Unrealized gain (loss) on available-for-sale securities Total Balance as of December 31, 2017 $ 30,962 $ 882 $ 31,844 Reclassification for impact of U.S. tax rate change — 161 161 Other comprehensive income (loss) 1,238 (936 ) 302 Balance as of June 30, 2018 $ 32,200 $ 107 $ 32,307

FINANCING ARRANGEMENTS

FINANCING ARRANGEMENTS	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
FINANCING ARRANGEMENTS	FINANCING ARRANGEMENTS Convertible Senior Notes On April 4, 2016, the Company issued $250.0 million in aggregate principal amount of convertible senior notes (the "Notes") in a private placement to A-G Holdings, L.P. ("AGH"). Michael Angelakis, the chairman and chief executive officer of Atairos Group, Inc. ("Atairos"), joined the Company's Board of Directors in connection with the issuance of the Notes. Atairos controls the voting power of AGH. The net proceeds from this offering were $243.2 million after deducting issuance costs. The Notes bear interest at a rate of 3.25% per annum, payable annually in arrears on April 1 of each year, beginning on April 1, 2017. The Notes will mature on April 1, 2022, subject to earlier conversion or redemption. Each $1,000 of principal amount of the Notes initially is convertible into 185.1852 shares of common stock, which is equivalent to an initial conversion price of $5.40 per share, subject to adjustment upon the occurrence of specified events. Upon conversion, the Company can elect to settle the conversion value in cash, shares of its common stock, or any combination of cash and shares of its common stock. Holders of the Notes may convert their Notes at their option at any time until the close of business on the scheduled trading day immediately preceding the maturity date. In addition, if specified corporate events occur prior to the maturity date, the Company may be required to increase the conversion rate for holders who elect to convert based on the effective date of such event and the applicable stock price attributable to the event, as set forth in a table contained in the indenture governing the Notes (the "Indenture"). Based on the closing price of the Company's common stock of $4.30 as of June 30, 2018 , the if-converted value of the Notes was less than the principal amount. With certain exceptions, upon a fundamental change (as defined in the Indenture), the holders of the Notes may require the Company to repurchase all or a portion of their Notes for cash at a purchase price equal to the principal amount plus accrued and unpaid interest. In addition, the Company may redeem the Notes, at its option, at a purchase price equal to the principal amount plus accrued and unpaid interest on or after April 1, 2020, if the closing sale price of the common stock exceeds 150% of the then-current conversion price for 20 or more trading days in the 30 consecutive trading day period preceding the Company’s exercise of this redemption right. The Notes are senior unsecured obligations of the Company that rank equal in right of payment to all senior unsecured indebtedness of the Company and rank senior in right of payment to any indebtedness that is contractually subordinated to the Notes. The Indenture includes customary events of default. If an event of default, as defined in the Indenture, occurs and is continuing, the principal amount of the Notes and any accrued and unpaid interest may be declared immediately due and payable. In the case of bankruptcy or insolvency, the principal amount of the Notes and any accrued and unpaid interest would automatically become immediately due and payable. The Company has separated the Notes into their liability and equity components in the accompanying condensed consolidated balance sheet. The carrying amount of the liability component was calculated by measuring the fair value of a similar liability that does not have an associated conversion feature. The carrying amount of the equity component, representing the conversion option, was determined by deducting the fair value of the liability component from the principal amount of the Notes. The difference between the principal amount of the Notes and the liability component (the "debt discount") is amortized to interest expense at an effective interest rate of 9.75% over the term of the Notes. The equity component of the Notes is included in additional paid-in capital in the condensed consolidated balance sheet and is not remeasured as long as it continues to meet the conditions for equity classification. The Company incurred transaction costs of approximately $6.8 million related to the issuance of the Notes. Those transaction costs were allocated to the liability and equity components in the same manner as the allocation of the proceeds from the Notes. Transaction costs attributable to the liability component of $4.8 million were recorded as a debt discount in the condensed consolidated balance sheet and are being amortized to interest expense over the term of the Notes. Transaction costs attributable to the equity component of $2.0 million were recorded in stockholders' equity as a reduction of the equity component. The carrying amount of the Notes consisted of the following as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Liability component: Principal amount $ 250,000 $ 250,000 Less: debt discount (54,441 ) (60,247 ) Net carrying amount of liability component $ 195,559 $ 189,753 Net carrying amount of equity component $ 67,014 $ 67,014 The estimated fair value of the Notes as of June 30, 2018 and December 31, 2017 was $273.8 million and $285.6 million , respectively, and was determined using a lattice model. The Company classified the fair value of the Notes as a Level 3 measurement due to the lack of observable market data over fair value inputs such as its stock price volatility over the term of the Notes and its cost of debt. As of June 30, 2018 , the remaining term of the Notes is approximately 3.75 years. During the three and six months ended June 30, 2018 and 2017 , the Company recognized interest costs on the Notes as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Contractual interest (3.25% of the principal amount per annum) $ 2,032 $ 2,032 $ 4,064 $ 4,064 Amortization of debt discount 2,940 2,655 5,806 5,242 Total $ 4,972 $ 4,687 $ 9,870 $ 9,306 Note Hedges and Warrants In May 2016, the Company purchased convertible note hedges with respect to its common stock for a cost of $59.1 million from certain bank counterparties. The convertible note hedges provide the Company with the right to purchase up to 46.3 million shares of the Company's common stock at an initial strike price of $5.40 per share, which corresponds to the initial conversion price of the Notes, and are exercisable by the Company upon conversion of the Notes. The convertible note hedges are intended to reduce the potential economic dilution upon conversion of the Notes. The convertible note hedges are separate transactions and are not part of the terms of the Notes. Holders of the Notes do not have any rights with respect to the convertible note hedges. In May 2016, the Company also sold warrants for total cash proceeds of $35.5 million to certain bank counterparties. The warrants provide the counterparties with the right to purchase up to 46.3 million shares of the Company's common stock at a strike price of $8.50 per share. The warrants expire on various dates between July 1, 2022 and August 26, 2022 and are exercisable on their expiration dates. The warrants are separate transactions and are not part of the terms of the Notes or convertible note hedges. Holders of the Notes and convertible note hedges do not have any rights with respect to the warrants. The amounts paid and received for the convertible note hedges and warrants were recorded in additional paid-in capital in the condensed consolidated balance sheets as of June 30, 2018 and December 31, 2017 . The convertible note hedges and warrants are not remeasured as long as they continue to meet the conditions for equity classification. The amounts paid for the convertible note hedges are tax deductible over the term of the Notes, while the proceeds received from the warrants are not taxable. Under the if-converted method, the shares of common stock underlying the conversion option in the Notes are included in the diluted earnings per share denominator and the interest expense on the Notes, net of tax, is added to the numerator. However, upon conversion, there will be no economic dilution from the Notes, as exercise of the convertible note hedges eliminates any dilution from the Notes that would have otherwise occurred when the price of the Company’s common stock exceeds the conversion price. Taken together, the purchase of the convertible note hedges and sale of warrants are intended to offset any actual dilution from the conversion of the Notes and to effectively increase the overall conversion price from $5.40 to $8.50 per share. Revolving Credit Agreement The Company's amended and restated senior secured revolving credit agreement (the "Amended and Restated Credit Agreement") provides for aggregate principal borrowings of up to $250.0 million and matures in June 2019. Borrowings under the Amended and Restated Credit Agreement bear interest, at the Company's option, at a rate per annum equal to the Alternate Base Rate or Adjusted LIBO Rate (each as defined in the Amended and Restated Credit Agreement) plus an additional margin ranging between 0.50% and 2.25% . The Company is required to pay quarterly commitment fees ranging from 0.25% to 0.40% per annum of the average daily amount of unused commitments available under the Amended and Restated Credit Agreement. The Amended and Restated Credit Agreement also provides for the issuance of up to $45.0 million in letters of credit, provided that the sum of outstanding borrowings and letters of credit do not exceed the maximum funding commitment of $250.0 million . The Amended and Restated Credit Agreement is secured by substantially all of the Company's and its subsidiaries' tangible and intangible assets, including a pledge of 100% of the outstanding capital stock of substantially all of its direct and indirect domestic subsidiaries and 65% of the shares or equity interests of first-tier foreign subsidiaries and each U.S. entity whose assets substantially consist of capital stock and/or intercompany debt of one or more foreign subsidiaries, subject to certain exceptions. Certain of the Company's domestic subsidiaries are guarantors under the Amended and Restated Credit Agreement. The Amended and Restated Credit Agreement contains various customary restrictive covenants that limit the Company's ability to, among other things: incur additional indebtedness; make dividend and other restricted payments, including share repurchases; enter into sale and leaseback transactions; make investments, loans or advances; grant or incur liens on assets; sell assets; engage in mergers, consolidations, liquidations or dissolutions; and engage in transactions with affiliates. The Amended and Restated Credit Agreement requires the Company to maintain compliance with specified financial covenants, comprised of a minimum fixed charge coverage ratio, a maximum leverage ratio, a maximum senior secured indebtedness ratio and a minimum liquidity ratio, each as set forth in the Amended and Restated Credit Agreement. The Company is also required to maintain, as of the last day of each fiscal quarter, unrestricted cash of at least $400.0 million , including $200.0 million in accounts held with lenders under the Amended and Restated Credit Agreement or their affiliates. Non-compliance with these covenants may result in termination of the commitments under the Amended and Restated Credit Agreement and any then outstanding borrowings may be declared due and payable immediately. The Company has the right to terminate the Amended and Restated Credit Agreement or reduce the available commitments at any time. As of June 30, 2018 and December 31, 2017 , the Company had no borrowings and had outstanding letters of credit of $18.6 million and $22.7 million , respectively, under the Amended and Restated Credit Agreement.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Except for the changes set forth below, the Company's commitments as of June 30, 2018 and through the date these condensed consolidated financial statements were issued did not materially change from the amounts set forth in the Company's 2017 Annual Report on Form 10-K. Leases In May 2018, the Company entered into a new office lease for one of its foreign locations. As of June 30, 2018 , the future payments under that operating lease for each of the next five years and thereafter are as follows (in thousands): Remaining amounts in 2018 $ 1,296 2019 2,592 2020 2,592 2021 2,592 2022 2,592 Thereafter 5,832 Total minimum lease payments $ 17,496 Other Contractual Commitments In the first quarter 2018, the Company entered into a non-cancelable arrangement for cloud computing services. As of June 30, 2018 , future payments under that contractual obligation are as follows (in thousands): Remaining amounts in 2018 $ — 2019 3,400 2020 3,400 2021 3,400 2022 3,400 Total $ 13,600 Legal Matters and Other Contingencies From time to time, the Company is party to various legal proceedings incident to the operation of its business. For example, the Company currently is involved in proceedings brought by former employees and merchants, intellectual property infringement suits, customer lawsuits, consumer class actions and suits alleging, among other things, violations of state consumer protection or privacy laws. The following is a brief description of significant legal proceedings. On March 2, 2016, International Business Machines Corporation ("IBM") filed a complaint in the United States District Court for the District of Delaware against the Company (the "Delaware Action"). In the Delaware Action, IBM alleges that the Company has infringed and continues to willfully infringe certain IBM patents that IBM claims relate to the presentation of applications and advertising in an interactive service, preserving state information in online transactions and single sign-on processes in a computing environment and seeks damages (including a request that the amount of compensatory damages be trebled), injunctive relief and costs and reasonable attorneys’ fees. Trial commenced in the Delaware Action on July 16, 2018. On July 27, 2018, a jury in this matter returned a verdict finding the Company willfully infringed each of these patents and awarded damages of $82.5 million to IBM. The court has the discretion to enhance this award for willfulness, impose interest, impose a continuing royalty for the two unexpired patents or award injunctive relief. The court also has the discretion to reduce or vacate the damages award or enter judgment for the Company on some or all of the claims notwithstanding the jury verdict. The Company intends to seek to overturn the verdict and reduce the damages award through post-trial motions and appeal. For the three months ended June 30, 2018, the Company recorded a $75.0 million charge to increase its contingent liability for this matter. That charge is classified within Selling, general and administrative in the accompanying condensed consolidated statement of operations. On May 9, 2016, the Company filed a complaint in the United States District Court for the Northern District of Illinois against IBM (the "Illinois Action"). The Company alleges that IBM has infringed and continues to willfully infringe one of the Company’s patents relating to location-based services. The Company intends to seek damages and injunctive relief for IBM’s infringement of this patent. On December 20, 2016, IBM filed a motion to dismiss this case, and the court denied that motion. The court held a Markman hearing on April 3, 2017, but has not yet construed the claims. On May 18, 2017, IBM filed two petitions for inter partes review with the United States Patent and Trademark Office seeking to invalidate the Company’s patent relating to location-based services. The Company filed its preliminary responses on September 6, 2017. The Patent Office denied one petition and instituted a review of the Company’s patent in response to the other petition, but such review did not include all claims requested by IBM. On May 1, 2018, the Patent Office stated that it would institute a review of the claims that were not previously under review based on a recent Supreme Court decision (SAS Institute, Inc. v. Iancu) finding that the Patent Office must institute a review of either all or none of claims petitioners seek to review. A trial date is not yet set in the Illinois Action. The Company plans to vigorously defend against the challenges to the Company’s patent in the Illinois Action. In addition, other third parties have from time to time claimed, and others may claim in the future, that the Company has infringed their intellectual property rights. The Company is subject to intellectual property disputes, including patent infringement claims, and expects that it will increasingly be subject to intellectual property infringement claims as its services expand in scope and complexity. The Company has in the past litigated such claims, and the Company is presently involved in several patent infringement and other intellectual property-related claims (including the IBM matter described above), including pending litigation or trademark disputes relating to, for example, the Company's Goods category, some of which could involve potentially substantial claims for damages or injunctive relief. The Company may also become more vulnerable to third-party claims as laws such as the Digital Millennium Copyright Act are interpreted by the courts, and as the Company becomes subject to laws in jurisdictions where the underlying laws with respect to the potential liability of online intermediaries are either unclear or less favorable. The Company believes that additional lawsuits alleging that it has violated patent, copyright or trademark laws will be filed against it. Intellectual property claims, whether meritorious or not, are time consuming and often costly to resolve, could require expensive changes in the Company's methods of doing business or the goods it sells, or could require it to enter into costly royalty or licensing agreements. The Company also is subject to consumer claims or lawsuits relating to alleged violations of consumer protection or privacy rights and statutes, some of which could involve potentially substantial claims for damages, including statutory or punitive damages. Consumer and privacy related claims or lawsuits, whether meritorious or not, could be time consuming, result in costly litigation, damage awards, fines and penalties, injunctive relief or increased costs of doing business through adverse judgment or settlement, or require the Company to change its business practices, sometimes in expensive ways. The Company also is subject to, or in the future may become subject to, a variety of regulatory inquiries, audits, and investigations across the jurisdictions where the Company conducts its business, including, for example, inquiries related to consumer protection, employment matters and/or hiring practices, marketing practices, tax, unclaimed property and privacy rules and regulations. Any regulatory actions against the Company, whether meritorious or not, could be time consuming, result in costly litigation, damage awards, fines and penalties, injunctive relief or increased costs of doing business through adverse judgment or settlement, require the Company to change its business practices in expensive ways, require significant amounts of management time, result in the diversion of significant operational resources or otherwise harm the Company's business. The Company establishes an accrued liability for loss contingencies related to legal and regulatory matters when the loss is both probable and reasonably estimable. Those accruals represent management's best estimate of probable losses and, in such cases, there may be an exposure to loss in excess of the amounts accrued. For certain of the matters described above, there are inherent and significant uncertainties based on, among other factors, the stage of the proceedings, developments in the applicable facts of law, or the lack of a specific damage claim. However, the Company believes that the amount of reasonably possible losses in excess of the amounts accrued for those matters would not have a material adverse effect on its business, consolidated financial position, results of operations or cash flows. The Company's accrued liabilities for loss contingencies related to legal and regulatory matters may change in the future as a result of new developments, including, but not limited to, the occurrence of new legal matters, changes in the law or regulatory environment, adverse or favorable rulings, newly discovered facts relevant to the matter, or changes in the strategy for the matter. Regardless of the outcome, litigation and other regulatory matters can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources and other factors. Indemnifications In connection with the dispositions of the Company's operations in Latin America (see Note 3 , Discontinued Operations and Other Business Dispositions ), the Company agreed to indemnify the buyer for certain tax and other matters. The indemnification liabilities were initially recorded at their fair value, estimated to be $5.4 million using a probability-weighted expected cash flow approach, upon closing of the transactions as an adjustment to the net loss on the dispositions within discontinued operations. The Company estimates that the total amount of obligations that are reasonably possible to arise under the indemnifications in excess of amounts accrued as of June 30, 2018 is approximately $18.0 million . In the normal course of business to facilitate transactions related to its operations, the Company indemnifies certain parties, including employees, lessors, service providers, merchants, and counterparties to investment agreements and asset and stock purchase agreements with respect to various matters. The Company has agreed to hold certain parties harmless against losses arising from a breach of representations or covenants, or other claims made against those parties. These agreements may limit the time within which an indemnification claim can be made and the amount of the claim. The Company is also subject to increased exposure to various claims as a result of its divestitures and acquisitions, particularly in cases where the Company is entering into new businesses in connection with such acquisitions. The Company may also become more vulnerable to claims as it expands the range and scope of its services and is subject to laws in jurisdictions where the underlying laws with respect to potential liability are either unclear or less favorable. In addition, the Company has entered into indemnification agreements with its officers, directors and underwriters, and the Company's bylaws contain similar indemnification obligations that cover officers, directors, employees and other agents. Except as noted above, it is not possible to determine the maximum potential amount under these indemnification agreements due to the limited history of prior indemnification claims and the unique facts and circumstances involved in each particular agreement. Historically, any payments that the Company has made under these agreements have not had a material impact on the operating results, financial position or cash flows of the Company.

STOCKHOLDERS' EQUITY AND COMPEN

STOCKHOLDERS' EQUITY AND COMPENSATION ARRANGEMENTS	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCKHOLDERS' EQUITY AND COMPENSATION ARRANGEMENTS	STOCKHOLDERS' EQUITY AND COMPENSATION ARRANGEMENTS The Company's Board of Directors (the "Board") has the authority, without approval by the stockholders, to issue up to a total of 50,000,000 shares of preferred stock in one or more series. The Board may establish the number of shares to be included in each such series and may fix the designations, preferences, powers and other rights of the shares of a series of preferred stock. The Board could authorize the issuance of preferred stock with voting or conversion rights that could dilute the voting power or rights of the holders of its common stock. As of June 30, 2018 and December 31, 2017 , there were no shares of preferred stock outstanding. Common Stock Pursuant to the Company's restated certificate of incorporation, the Board has the authority to issue up to a total of 2,010,000,000 shares of common stock. Each holder of common stock shall be entitled to one vote for each such share on any matter that is submitted to a vote of stockholders. In addition, holders of the common stock will vote as a single class of stock on any matter that is submitted to a vote of stockholders. Share Repurchase Program In May 2018, the Board authorized the Company to repurchase up to $300.0 million of its common stock under a new share repurchase program. The Company's prior share repurchase program expired in April 2018. During the three and six months ended June 30, 2018 , the Company did not purchase any shares under those share repurchase programs. The timing and amount of share repurchases, if any, will be determined based on market conditions, limitations under the Amended and Restated Credit Agreement, share price and other factors, and the share repurchase program may be terminated at any time. Groupon, Inc. Stock Plans The Groupon, Inc. Stock Plans (the "Plans") are administered by the Compensation Committee of the Board (the "Compensation Committee"), which determines the number of awards to be issued, the corresponding vesting schedule and the exercise price for options. As of June 30, 2018 , 52,436,687 shares of common stock were available for future issuance under the Plans. The stock-based compensation expense related to stock awards issued under the Plans and acquisition-related awards are presented within the following line items of the condensed consolidated statements of operations for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Cost of revenue $ 288 $ 794 $ 684 $ 1,457 Marketing 1,763 2,230 3,557 4,032 Selling, general and administrative 14,215 18,368 31,303 35,553 Other income (expense) 52 48 100 99 Total stock-based compensation expense $ 16,318 $ 21,440 $ 35,644 $ 41,141 The Company also capitalized $2.0 million and $1.8 million of stock-based compensation for the three months ended June 30, 2018 and 2017 , respectively, and $3.7 million and $3.3 million for the six months ended June 30, 2018 and 2017 , respectively, in connection with internally-developed software. As of June 30, 2018 , $138.1 million of unrecognized compensation costs related to unvested employee stock awards are expected to be recognized over a remaining weighted-average period of 1.44 years. Employee Stock Purchase Plan The Company is authorized to grant up to 10,000,000 shares of common stock under its employee stock purchase plan ("ESPP"). For the six months ended June 30, 2018 and 2017 , 746,773 and 877,845 shares of common stock, respectively, were issued under the ESPP. Restricted Stock Units The restricted stock units granted under the Plans generally have vesting periods between one and four years. Restricted stock units are amortized on a straight-line basis over the requisite service period. The table below summarizes activity regarding unvested restricted stock units granted under the Plans for the six months ended June 30, 2018 : Restricted Stock Units Weighted-Average Grant Date Fair Value (per unit) Unvested at December 31, 2017 28,939,110 $ 4.32 Granted 14,631,563 4.76 Vested (7,507,084 ) 4.41 Forfeited (3,202,754 ) 4.26 Unvested at June 30, 2018 32,860,835 4.51 Performance Share Units The performance share units granted under the Plans vest in shares of the Company's common stock upon the achievement of financial and operational targets specified in the respective award. The awards are subject to both continued employment through the performance period dictated by the award and certification by the Compensation Committee that the specified financial and operational targets have been achieved. During the six months ended June 30, 2018 , the Company granted performance share units for which the maximum number of common shares issuable upon vesting of those performance share units is 7,706,474 shares, the weighted-average grant date fair value was $4.89 per unit and the total grant date fair value of the shares for which the performance conditions are expected to be met was $16.6 million . During the six months ended June 30, 2018 , 278,635 shares of the Company's common stock were issued related to performance share units granted in the previous year following the Compensation Committee's certification of the Company's financial and operational metrics for the year ended December 31, 2017. The weighted-average grant date fair value of those units was $3.78 per share. Performance Bonus Awards If bonus amounts earned under the Company's primary employee bonus plans exceed targeted bonus amounts because specified financial metrics of the Company exceed the performance conditions set forth in those plans, such excess is required to be settled in the Company's common stock. The Company's obligation to issue shares for employee bonus amounts exceeding the specified bonus targets is accounted for separately as a liability-classified stock-based compensation arrangement with performance conditions. During the six months ended June 30, 2018 , 1,240,379 shares of the Company's common stock were issued related to performance bonus awards granted in the previous year following the Compensation Committee's certification of the Company's financial and operational metrics for the year ended December 31, 2017. The fair value of the Company's common stock on the date of the Compensation Committee's certification was $5.20 per share. Stock Options The exercise price of stock options granted is equal to the fair value of the underlying stock on the date of grant. The contractual term for stock options expires ten years from the grant date. Stock options generally vested over a three or four -year period, with 25% of the awards vesting after one year and the remainder of the awards vesting on a monthly or quarterly basis thereafter. The table below summarizes the stock option activity for the six months ended June 30, 2018 : Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) (1) Outstanding and exercisable at December 31, 2017 885,580 $ 0.62 1.76 $ 3,967 Exercised (667,743 ) 0.10 Forfeited — — Outstanding and exercisable at June 30, 2018 217,837 1.81 1.88 $ 542 (1) The aggregate intrinsic value of options outstanding and exercisable represents the total pretax intrinsic value (the difference between the fair value of the Company's stock on the last day of each period and the exercise price, multiplied by the number of options where the fair value exceeds the exercise price) that would have been received by the option holders had all option holders exercised their options as of June 30, 2018 and December 31, 2017 , respectively.

REVENUE RECOGNITION

REVENUE RECOGNITION	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION Product and service revenue are generated from sales transactions through the Company's online marketplaces in three primary categories: Local, Goods and Travel. Product revenue is earned from direct sales of merchandise inventory to customers and includes any related shipping fees. Service revenue primarily represents the net commissions earned by the Company from selling goods and services provided by third-party merchants. Those marketplace transactions generally involve the online delivery of a voucher that can be redeemed by the purchaser with the third-party merchant for goods or services (or for discounts on goods or services). To a lesser extent, service revenue also includes commissions earned when customers make purchases with retailers using digital coupons accessed through the Company's websites and mobile applications. Additionally, in the United States the Company has recently been developing and testing voucherless offerings that are linked to customer credit cards. Customers claim those voucherless merchant offerings through the Company's online marketplaces and earn cash back on their credit card statements when they transact with the related merchants, who pay the Company commissions for such transactions. In connection with most of our product and service revenue transactions, the Company collects cash from credit card payment processors shortly after a sale occurs. For transactions in which the Company earns commissions when customers make purchases with retailers using digital coupons accessed through its websites and mobile applications, the Company generally collects payment from affiliate networks on terms ranging from 30 to 150 days. As discussed in Note 1 , Description of Business and Basis of Presentation , the Company previously referred to its product revenue and service revenue as "direct revenue" and "third-party and other revenue," respectively. Adoption of ASC Topic 606, Revenue from Contracts with Customers On January 1, 2018, the Company adopted Accounting Standards Codification Topic 606, Revenue from Contracts with Customers ("Topic 606") using the modified retrospective method. Beginning on January 1, 2018, results are presented in accordance with the Company's revised policies, while prior period amounts are not adjusted and continue to be reported in accordance with the Company's historical policies. The adoption of Topic 606 did not significantly impact the Company's presentation of revenue on a gross or net basis. The following changes resulted from the adoption of Topic 606: • For merchant agreements with redemption payment terms, the merchant is not paid its share of the sale price for a voucher sold through one of the Company's online marketplaces until the customer redeems the related voucher. If the customer does not redeem a voucher with such merchant payment terms, the Company retains all of the gross billings for that voucher, rather than retaining only its net commission. Prior to its adoption of Topic 606, the Company recognized that variable consideration from unredeemed vouchers and derecognized the related accrued merchant payables when its legal obligation to the merchant expired, which the Company believes is shortly after the voucher expiration date in most jurisdictions. Following its adoption of Topic 606, the Company estimates the variable consideration from vouchers that will not ultimately be redeemed and recognizes that amount as revenue at the time of sale, rather than when the Company's legal obligation expires. The Company estimates variable consideration from unredeemed vouchers using its historical voucher redemption experience. Most vouchers sold through the Company's marketplace in the United States do not have expiration dates and redemption payment terms were not widely used in that jurisdiction before 2017, so the Company's North America segment did not have variable consideration from unredeemed vouchers in prior periods. • Prior to its adoption of Topic 606, the Company expensed the incremental costs to obtain contracts with third-party merchants, such as sales commissions, as incurred. Following its adoption of Topic 606, those costs are deferred and recognized over the expected period of the merchant arrangement, generally from 12 to 18 months. • Prior to its adoption of Topic 606, the Company recognized breakage income for unused customer credits when they expired or were forfeited. Following its adoption of Topic 606, breakage income from customer credits that are not expected to be used is estimated and recognized as revenue in proportion to the pattern of redemption for customer credits that are used. • Prior to its adoption of Topic 606, the Company deferred the revenue from hotel reservation offerings until the customer's stay commenced. Following its adoption of Topic 606, revenue from hotel reservation offerings is recognized at the time the reservation is made, net of an allowance for estimated cancellations. • Prior to its adoption of Topic 606, the Company classified refunds on service revenue transactions for which the merchant's share of the refund amount is not recoverable as a cost of revenue. Following its adoption of Topic 606, those refunds are classified as a reduction of revenue. • Prior to its adoption of Topic 606, the Company classified credits issued to consumers for relationship purposes as a marketing expense. Following its adoption of Topic 606, those credits are classified as a reduction of revenue. The Company recorded a net reduction to its opening accumulated deficit of $88.9 million , which is net of a $6.7 million income tax effect, as of January 1, 2018 due to the cumulative impact of adopting Topic 606. The following table summarizes balance sheet accounts impacted by the cumulative effect of adopting Topic 606 (in thousands): Account Increase (decrease) to beginning accumulated deficit Prepaid expenses and other current assets $ (4,007 ) Other non-current assets (10,223 ) Accrued merchant and supplier payables (64,970 ) Accrued expenses and other current liabilities (13,188 ) Other non-current liabilities 3,443 Effect on beginning accumulated deficit $ (88,945 ) See Note 2 , Adoption of New Accounting Standards , for additional information about the Company's revenue recognition policies before and after the adoption of Topic 606. Impacts on Condensed Consolidated Financial Statements The following tables summarize the impacts of adopting Topic 606 on the Company's condensed consolidated financial statements as of and for the three and six months ended June 30, 2018 (in thousands): Condensed Consolidated Balance Sheet June 30, 2018 As reported Adjustments Balances without adoption of Topic 606 Total assets $ 1,488,700 $ (11,638 ) $ 1,477,062 Total liabilities 1,217,563 86,124 1,303,687 Total equity 271,137 (97,762 ) 173,375 C ondensed Consolidated Statements of Operations Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As reported Adjustments Balances without adoption of Topic 606 As reported Adjustments Balances without adoption of Topic 606 Revenue: Service revenue (1)(2) $ 295,652 $ 6,001 $ 301,653 $ 597,449 $ 4,222 $ 601,671 Product revenue 321,744 — 321,744 646,487 — 646,487 Total revenue 617,396 6,001 623,397 1,243,936 4,222 1,248,158 Cost of revenue: Service cost of revenue (3) 30,230 7,043 37,273 61,375 13,318 74,693 Product cost of revenue 263,508 — 263,508 534,018 — 534,018 Cost of revenue (3) 293,738 7,043 300,781 595,393 13,318 608,711 Gross profit 323,658 (1,042 ) 322,616 648,543 (9,096 ) 639,447 Operating expenses: Marketing (4) 94,178 2,134 96,312 193,334 3,707 197,041 Selling, general and administrative (5) 294,124 (1,227 ) 292,897 516,185 (2,491 ) 513,694 Restructuring charges (399 ) — (399 ) (116 ) — (116 ) Total operating expenses 387,903 907 388,810 709,403 1,216 710,619 Income (loss) from operations (64,245 ) (1,949 ) (66,194 ) (60,860 ) (10,312 ) (71,172 ) Other income (expense), net (26,457 ) — (26,457 ) (34,972 ) — (34,972 ) Income (loss) before provision (benefit) for income taxes (90,702 ) (1,949 ) (92,651 ) (95,832 ) (10,312 ) (106,144 ) Provision (benefit) for income taxes (6) 1,552 886 2,438 (783 ) (133 ) (916 ) Net income (loss) $ (92,254 ) $ (2,835 ) $ (95,089 ) $ (95,049 ) $ (10,179 ) $ (105,228 ) (1) For the three months ended June 30, 2018 , reflects a $9.2 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, and an increase of $0.5 million related to the timing of recognition of revenue from hotel reservation offerings, partially offset by decreases of $2.9 million related to the timing of recognition of variable consideration from unredeemed vouchers and $0.8 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used. (2) For the six months ended June 30, 2018 , reflects a $17.0 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, partially offset by decreases of $8.5 million related to the timing of recognition of variable consideration from unredeemed vouchers, $2.8 million related to the timing of recognition of revenue from hotel reservation offerings and $1.5 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used. (3) Reflects an increase for refunds on service revenue transactions for which the merchant's share is not recoverable, which are classified as a reduction of revenue under Topic 606. (4) Reflects an increase for customer credits issued for relationship purposes, which are classified as a reduction of revenue under Topic 606. (5) Reflects the amortization of deferred contract acquisition costs in excess of amounts capitalized in the current period. (6) As discussed in Note 13 , Income Taxes , for the six months ended June 30, 2018 , the Company recognized an income tax benefit of $6.4 million resulting from the impact of adopting Topic 606 on intercompany activity in certain foreign jurisdictions. That income tax benefit is not reflected in this table, which presents the direct impacts of adopting Topic 606. Segment and Category Information Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As reported Adjustments Balances without adoption of Topic 606 As reported Adjustments Balances without adoption of Topic 606 North America Service revenue: Local $ 185,870 $ 913 $ 186,783 $ 373,281 $ 4,526 $ 377,807 Goods 3,796 95 3,891 8,670 95 8,765 Travel 19,888 678 20,566 39,972 (2,401 ) 37,571 Product revenue - Goods 170,710 — 170,710 351,597 — 351,597 Total North America revenue 380,264 1,686 381,950 773,520 2,220 775,740 International Service revenue: Local 71,425 3,946 75,371 146,003 2,500 148,503 Goods 4,967 (557 ) 4,410 8,381 (796 ) 7,585 Travel 9,706 926 10,632 21,142 298 21,440 Product revenue - Goods 151,034 — 151,034 294,890 — 294,890 Total International revenue 237,132 4,315 241,447 470,416 2,002 472,418 Consolidated Service revenue: Local 257,295 4,859 262,154 519,284 7,026 526,310 Goods 8,763 (462 ) 8,301 17,051 (701 ) 16,350 Travel 29,594 1,604 31,198 61,114 (2,103 ) 59,011 Product revenue - Goods 321,744 — 321,744 646,487 — 646,487 Total Consolidated Revenue $ 617,396 $ 6,001 $ 623,397 $ 1,243,936 $ 4,222 $ 1,248,158 Contract Balances The following table summarizes the activity in revenue deferred from contracts with customers for the six months ended June 30, 2018 (in thousands): Deferred Revenue Balance as of January 1, 2018 $ 25,763 Revenue deferred 21,802 Revenue recognized (25,364 ) Foreign currency translation (399 ) Balance as of June 30, 2018 $ 21,802 A substantial majority of our deferred revenue relates to product sales for which revenue will be recognized as the products are delivered to customers, generally within one week following the balance sheet date. The following table summarizes the activity in the liability for customer credits for the six months ended June 30, 2018 (in thousands): Customer Credits Balance as of January 1, 2018 $ 19,414 Credits issued 67,025 Credits redeemed (1) (57,074 ) Breakage revenue recognized (10,961 ) Foreign currency translation (88 ) Balance as of June 30, 2018 $ 18,316 (1) Customer credits can be redeemed through the Company's online marketplaces for goods or services provided by a third-party merchant or for merchandise inventory sold by the Company. When customer credits are redeemed for goods or services provided by a third-party merchant, service revenue is recognized on a net basis as the difference between the carrying amount of the customer credit liability derecognized and the amount due to the merchant for the related transaction. When customer credits are redeemed for merchandise inventory sold by the Company, product revenue is recognized on a gross basis equal to the amount of the customer credit liability derecognized. Customer credits are primarily used within one year of issuance.

RESTRUCTURING

RESTRUCTURING	6 Months Ended
	Jun. 30, 2018
Restructuring and Related Activities [Abstract]
RESTRUCTURING	RESTRUCTURING In September 2015, the Company commenced a restructuring plan relating primarily to workforce reductions in its international operations. The Company has also undertaken workforce reductions in its North America segment. In addition to workforce reductions in its ongoing markets, the Company ceased operations in 17 countries within its International segment as part of the restructuring plan between September 2015 and March 2016. Those country exits, which generally comprised the Company's smallest international markets, resulted from a series of separate decisions made at different times during that period that were not part of an overall strategic shift. Costs related to the restructuring plan are classified as Restructuring charges on the condensed consolidated statements of operations. The actions under the Company's restructuring plan were completed as of September 30, 2017 and substantially all of the remaining cash payments for actions under that plan are expected to be disbursed through December 31, 2018. The Company incurred cumulative costs for employee severance and benefits and other exit costs of $80.1 million under the plan since its inception in September 2015. In addition to those costs, the Company incurred cumulative long-lived asset impairment charges of $7.5 million resulting from its restructuring activities. The following tables summarize the costs incurred by segment related to the Company’s restructuring plan for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, 2018 Employee Severance and Benefit Costs (1) Other Exit Costs (1) Total Restructuring Charges (Credits) North America $ — $ 177 $ 177 International (576 ) — (576 ) Consolidated $ (576 ) $ 177 $ (399 ) Six Months Ended June 30, 2018 Employee Severance and Benefit Costs (1) Other Exit Costs (1) Total Restructuring Charges (Credits) North America $ — $ 177 $ 177 International (346 ) 53 (293 ) Consolidated $ (346 ) $ 230 $ (116 ) Three Months Ended June 30, 2017 Employee Severance and Benefit Costs (2) Other Exit Costs Total Restructuring Charges North America $ 2,687 $ 288 $ 2,975 International 86 1,523 1,609 Consolidated $ 2,773 $ 1,811 $ 4,584 Six Months Ended June 30, 2017 Employee Severance and Benefit Costs (2) Other Exit Costs Total Restructuring Charges North America $ 4,465 $ 465 $ 4,930 International 609 1,776 2,385 Consolidated $ 5,074 $ 2,241 $ 7,315 (1) The $0.4 million and $0.1 million of restructuring credits for the three and six months ended June 30, 2018 , respectively, reflect changes in estimates related to prior actions. (2) The employee severance and benefit costs for the three and six months ended June 30, 2017 related to the termination of approximately 150 and 350 employees, respectively. The following table summarizes the restructuring liability activity for the six months ended June 30, 2018 (in thousands): Employee Severance and Benefit Costs Other Exit Costs Total Balance as of December 31, 2017 $ 3,817 $ 304 $ 4,121 Charges payable in cash (346 ) 230 (116 ) Cash payments (1,428 ) (53 ) (1,481 ) Foreign currency translation (67 ) — (67 ) Balance as of June 30, 2018 $ 1,976 $ 481 $ 2,457

INCOME TAXES

INCOME TAXES	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company's tax provision for interim periods is determined using an estimate of its annual effective tax rate, adjusted for discrete items. For the three months ended June 30, 2018 , the Company recorded an income tax expense from continuing operations of $1.6 million on a pretax loss from continuing operations of $90.7 million . For the three months ended June 30, 2017 , the Company recorded an income tax expense from continuing operations of $3.9 million on a pretax loss from continuing operations of $1.5 million . For the six months ended June 30, 2018 , the Company recorded an income tax benefit from continuing operations of $0.8 million on a pretax loss from continuing operations of $95.8 million . For the six months ended June 30, 2017 , the Company recorded an income tax expense from continuing operations of $8.5 million on a pretax loss from continuing operations of $17.8 million . The Company's U.S. Federal income tax rate is 21% for the three and six months ended June 30, 2018 and was 35% for the three and six months ended June 30, 2017 . The primary factor impacting the effective tax rate for the three and six months ended June 30, 2018 and 2017 was the pretax losses incurred in jurisdictions that have valuation allowances against their net deferred tax assets. The effective tax rate for the six months ended June 30, 2018 also reflected a $6.4 million income tax benefit resulting from the impact of adopting Topic 606 on intercompany activity in certain foreign jurisdictions. The Company is currently undergoing income tax audits in multiple jurisdictions. There are many factors, including factors outside of the Company's control, which influence the progress and completion of those audits. During the fourth quarter 2017, the Company received an income tax assessment and a notification of proposed assessment from the tax authorities in two foreign jurisdictions, totaling $134.5 million in the aggregate. The Company believes that the assessments, which primarily relate to transfer pricing on transactions occurring from 2011 to 2014, are without merit and it intends to vigorously defend itself in those matters. In addition to any potential increases in its liabilities for uncertain tax positions from the ultimate resolution of those assessments, the Company believes that it is reasonably possible that reductions of up to $40.6 million in unrecognized tax benefits may occur within the 12 months following June 30, 2018 upon closing of income tax audits or the expiration of applicable statutes of limitations. The Jobs Act was signed into law on December 22, 2017. The Company has made provisional estimates for the impact of the Jobs Act related to the re-measurement of deferred income taxes, valuation allowances, uncertain tax positions, and its assessment of permanently reinvested earnings. Those estimates may be impacted by the need for further analysis and future clarification and guidance regarding available tax accounting methods and elections, earnings and profits computations and state tax conformity to federal tax changes. Additionally, while the Company does not expect to incur the deemed repatriation tax, it has not yet finalized the related calculations. The Jobs Act also establishes global intangible low-taxed income ("GILTI") provisions that impose a tax on foreign income in excess of a deemed return on intangible assets of foreign corporations. The Company is in the process of evaluating the impact of taxes on GILTI and has not yet determined whether its accounting policy will be to recognize deferred taxes for basis differences that are expected to affect the amount of GILTI inclusion upon reversal or to recognize taxes on GILTI as an expense in the period incurred. In general, it is the practice and intention of the Company to reinvest the earnings of its non-U.S. subsidiaries in those operations. Additionally, while the Company does not expect to incur the deemed repatriation tax established by the Jobs Act, an actual repatriation from its non-U.S. subsidiaries could be subject to foreign and U.S. state income taxes. Aside from limited exceptions for which the related deferred tax liabilities recognized as of June 30, 2018 and December 31, 2017 are immaterial, the Company does not intend to distribute earnings of foreign subsidiaries for which it has an excess of the financial reporting basis over the tax basis of its investments and therefore has not recorded any deferred taxes related to such amounts. The actual tax cost resulting from a distribution would depend on income tax laws and circumstances at the time of distribution. Determination of the amount of unrecognized deferred tax liability related to the excess of the financial reporting basis over the tax basis of the Company's foreign subsidiaries is not practical due to the complexities associated with the calculation.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Fair value is defined under U.S. GAAP 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. Fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or a liability. To increase the comparability of fair value measures, the following hierarchy prioritizes the inputs in valuation methodologies used to measure fair value: Level 1 - Measurements that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets. Level 2 - Measurements that include other inputs that are directly or indirectly observable in the marketplace. Level 3 - Measurements derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. These fair value measurements require significant judgment. In determining fair value, the Company uses various valuation approaches within the fair value measurement framework. The valuation methodologies used for the Company's assets and liabilities measured at fair value and their classification in the valuation hierarchy are summarized below: Cash equivalents. Cash equivalents primarily consisted of AAA-rated money market funds. The Company classified cash equivalents as Level 1 due to the short-term nature of these instruments and measured the fair value based on quoted prices in active markets for identical assets. Fair value option investments and available-for-sale securities. To determine the fair value of its fair value option investments each period, the Company first estimates the fair value of each entity in its entirety. The Company primarily uses the discounted cash flow method, which is an income approach, to estimate the fair value of the investees. The key inputs to determining fair values under that approach are cash flow forecasts and discount rates. As of June 30, 2018 and December 31, 2017 , the Company applied discount rates of 21% and 22% , respectively, in its discounted cash flow valuations for Monster LP. The Company also uses a market approach valuation technique, which is based on market multiples of guideline companies, to determine the fair value of each entity. The discounted cash flow and market multiple valuations are then evaluated and weighted to determine the amount that is most representative of the fair value of each entity. Once the Company determines the fair value of each entity, it then determines the fair value of its specific investments in those entities. The entities have complex capital structures, so the Company applies an option-pricing model that considers the liquidation preferences of each investee’s respective classes of ownership interests to determine the fair value of the Company’s investment in each entity. The Company also has investments in redeemable preferred shares and convertible debt securities issued by nonpublic entities. The Company measures the fair value of those available-for-sale securities using the discounted cash flow method. The Company has classified its fair value option investments and its investments in available-for-sale securities as Level 3 due to the lack of observable market data over fair value inputs such as cash flow projections and discount rates. Increases in projected cash flows and decreases in discount rates contribute to increases in the estimated fair values of the fair value option investments and available-for-sale securities, whereas decreases in projected cash flows and increases in discount rates contribute to decreases in their fair values. Contingent consideration. The Company is subject to a contingent consideration arrangement to transfer a maximum payout in cash of $2.6 million to the former owners of a business acquired on April 30, 2018. See Note 4 , Business Combinations , for further discussion of that acquisition. Additionally, the Company had contingent obligations in prior periods to transfer cash to the former owners of a previous business acquisition if specified financial results were met (i.e. an earnout). Liabilities for contingent consideration are measured at fair value each reporting period, with the acquisition-date fair value included as part of the consideration transferred in the related business combination and subsequent changes in fair value recorded in earnings within Selling, general and administrative expense on the condensed consolidated statements of operations. The Company uses an income approach to value contingent consideration obligations based on the present value of probability-weighted future cash flows. The Company classifies the contingent consideration liabilities as Level 3 due to the lack of relevant observable market data over fair value inputs such as probability-weighting of payment outcomes. The following tables summarize the Company's assets that are measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 (in thousands): Fair Value Measurement at Reporting Date Using June 30, 2018 Quoted Prices in Active Markets for Significant Other Significant Assets: Fair value option investments $ 74,898 $ — $ — $ 74,898 Available-for-sale securities: Convertible debt securities 10,236 — — 10,236 Redeemable preferred shares 9,961 — — 9,961 Liabilities: Contingent Consideration 1,542 — — 1,542 Fair Value Measurement at Reporting Date Using December 31, 2017 Quoted Prices in Active Markets for Significant Other Significant Cash equivalents $ 137,975 $ 137,975 $ — $ — Fair value option investments 82,966 — — 82,966 Available-for-sale securities: Convertible debt securities 11,354 — — 11,354 Redeemable preferred shares 15,431 — — 15,431 The following table provides a roll-forward of the fair value of recurring Level 3 fair value measurements for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Assets Fair value option investments: Beginning Balance $ 77,933 $ 82,887 $ 82,966 $ 82,584 Total gains (losses) included in earnings (3,035 ) (1,448 ) (8,068 ) (1,145 ) Ending Balance $ 74,898 $ 81,439 $ 74,898 $ 81,439 Unrealized gains (losses) still held (1) $ (3,035 ) $ (1,448 ) $ (8,068 ) $ (1,145 ) Available-for-sale securities Convertible debt securities: Beginning Balance $ 11,070 $ 11,931 $ 11,354 $ 10,038 Purchase of convertible debt security — — — 1,612 Proceeds at maturity of convertible debt security — (1,843 ) — (1,843 ) Transfer to other equity investment upon conversion of convertible debt security (2,508 ) — (2,508 ) — Total gains (losses) included in other comprehensive income (loss) (541 ) (575 ) (1,042 ) (533 ) Total gains (losses) included in earnings (2) 2,215 1,355 2,432 1,594 Ending Balance $ 10,236 $ 10,868 $ 10,236 $ 10,868 Unrealized gains (losses) still held (1) $ 2,599 $ 512 $ 2,405 $ 816 Redeemable preferred shares: Beginning Balance $ 14,576 $ 17,788 $ 15,431 $ 17,444 Total gains (losses) included in other comprehensive income (loss) — (1,865 ) — (1,521 ) Impairments included in earnings (4,615 ) — (5,470 ) — Ending Balance $ 9,961 $ 15,923 $ 9,961 $ 15,923 Unrealized (losses) gains still held (1) $ (4,615 ) $ (1,865 ) $ (5,470 ) $ (1,521 ) Liabilities Contingent Consideration: Beginning Balance $ — $ 14,600 $ — $ 14,588 Issuance of contingent consideration in connection with acquisition 1,589 — 1,589 — Settlements of contingent consideration liabilities — (7,858 ) — (7,858 ) Reclass to non-fair value liabilities when no longer contingent — (6,778 ) — (6,778 ) Total losses (gains) included in earnings 14 36 14 48 Foreign currency translation (61 ) — (61 ) — Ending Balance $ 1,542 $ — $ 1,542 $ — Unrealized losses (gains) still held (1) $ (47 ) $ — $ (47 ) $ — (1) Represents the unrealized gains or losses recorded in earnings and/or other comprehensive income (loss) during the period for assets and liabilities classified as Level 3 that are still held (or outstanding) at the end of the period. (2) Represents a gain at maturity of a previously impaired convertible debt security, accretion of interest income and changes in the fair value of an embedded derivative. Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis Certain assets and liabilities are measured at fair value on a nonrecurring basis, including assets that are written down to fair value as a result of an impairment. The Company recorded a $4.6 million impairment of an other equity investment for the three months ended June 30, 2018 . To determine the fair value of the investment, the Company considered the financial condition of the investee and applied a market approach. The Company has classified the fair value measurement of that other equity investment as Level 3 because it involves significant unobservable inputs. The Company did not record any other nonrecurring fair value measurements after initial recognition for the three and six months ended June 30, 2018 and 2017 . Estimated Fair Value of Financial Assets and Liabilities Not Measured at Fair Value The following table presents the carrying amount and fair value of equity securities that were classified as cost method investments as of December 31, 2017 (in thousands): December 31, 2017 Carrying Amount Fair Value Cost method investments (1) $ 25,438 $ 32,792 (1) See Note 2 , Adoption of New Accounting Standards , and Note 6 , Investments , for information about the Company's adoption of ASU 2016-01 on January 1, 2018 and its impact on accounting for equity investments without readily determinable fair values that were previously subject to the cost method of accounting. The fair values of the Company's cost method investments were determined using the market approach or the income approach, depending on the availability of fair value inputs such as financial projections for the investees and market multiples for comparable companies. The Company classified the fair value measurements of its cost method investments as Level 3 measurements within the fair value hierarchy as of December 31, 2017 because they involve significant unobservable inputs such as cash flow projections and discount rates. The Company's other financial instruments not carried at fair value consist primarily of accounts receivable, restricted cash, accounts payable, accrued merchant and supplier payables and accrued expenses. The carrying values of those assets and liabilities approximate their respective fair values as of June 30, 2018 and December 31, 2017 due to their short-term nature.

INCOME (LOSS) PER SHARE

INCOME (LOSS) PER SHARE	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
INCOME (LOSS) PER SHARE	INCOME (LOSS) PER SHARE Basic net income (loss) per share is computed using the weighted-average number of common shares outstanding during the period. Diluted net income (loss) per share is computed using the weighted-average number of common shares and the effect of potentially dilutive securities outstanding during the period. Potentially dilutive securities include stock options, restricted stock units, performance share units, performance bonus awards, ESPP shares, warrants and convertible senior notes. If dilutive, those potentially dilutive securities are reflected in diluted net income (loss) per share by application of the treasury stock method, except for the convertible senior notes, which are subject to the if-converted method. The following table sets forth the computation of basic and diluted net income (loss) per share of common stock for the three and six months ended June 30, 2018 and 2017 (in thousands, except share amounts and per share amounts): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Basic and diluted net income (loss) per share: Numerator Net income (loss) - continuing operations $ (92,254 ) $ (5,403 ) $ (95,049 ) $ (26,272 ) Less: Net income (loss) attributable to noncontrolling interests 2,780 2,547 6,873 6,579 Net income (loss) attributable to common stockholders - continuing operations (95,034 ) (7,950 ) (101,922 ) (32,851 ) Net income (loss) attributable to common stockholders - discontinued operations — (1,376 ) — (889 ) Net income (loss) attributable to common stockholders $ (95,034 ) $ (9,326 ) $ (101,922 ) $ (33,740 ) Denominator Weighted-average common shares outstanding 565,284,705 559,762,180 563,502,954 560,978,712 Basic and diluted net income (loss) per share (1) : Continuing operations $ (0.17 ) $ (0.01 ) $ (0.18 ) $ (0.06 ) Discontinued operations 0.00 (0.01 ) 0.00 0.00 Basic and diluted net income (loss) per share $ (0.17 ) $ (0.02 ) $ (0.18 ) $ (0.06 ) (1) The potentially dilutive impacts of outstanding equity awards, warrants and convertible senior notes have been excluded from the calculation of dilutive net income (loss) per share for the three and six months ended June 30, 2018 and 2017 as their effect on net income (loss) per share from continuing operations was antidilutive. The following weighted-average potentially dilutive instruments are not included in the diluted net income (loss) per share calculations above because they would have had an antidilutive effect on the net income (loss) per share from continuing operations: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Restricted stock units 32,602,563 30,134,808 30,378,335 27,247,728 Other stock-based compensation awards 1,615,249 3,437,075 2,413,637 3,667,440 Convertible senior notes 46,296,300 46,296,300 46,296,300 46,296,300 Warrants 46,296,300 46,296,300 46,296,300 46,296,300 Total 126,810,412 126,164,483 125,384,572 123,507,768 The Company had outstanding performance share units as of June 30, 2018 and 2017 that were eligible to vest into shares of common stock subject to the achievement of specified performance conditions. Contingently issuable shares are excluded from the computation of diluted earnings per share if, based on current period results, the shares would not be issuable if the end of the reporting period were the end of the contingency period. There were up to 7,706,474 and 2,505,346 shares of common stock issuable upon vesting of outstanding performance share units as of June 30, 2018 and 2017 , respectively, that were excluded from the table above as the performance conditions were not satisfied as of the end of the respective periods.

SEGMENT INFORMATION

SEGMENT INFORMATION	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION The segment information reported in the tables below reflects the operating results that are regularly reviewed by the Company's chief operating decision maker to assess performance and make resource allocation decisions. The Company's operations are organized into two segments: North America and International. The following table summarizes revenue by reportable segment and category for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 North America Service revenue: Local $ 185,870 $ 207,534 $ 373,281 $ 408,079 Goods 3,796 4,112 8,670 5,816 Travel 19,888 22,320 39,972 42,782 Product revenue - Goods 170,710 217,946 351,597 468,592 Total North America revenue (1) 380,264 451,912 773,520 925,269 International Service revenue: Local 71,425 66,108 146,003 129,683 Goods 4,967 4,984 8,381 9,268 Travel 9,706 10,796 21,142 21,798 Product revenue - Goods 151,034 128,819 294,890 250,227 Total International revenue (1) $ 237,132 $ 210,707 $ 470,416 $ 410,976 (1) North America includes revenue from the United States of $371.1 million and $442.7 million for the three months ended June 30, 2018 and 2017 , respectively, and $756.5 million and $907.4 million for the six months ended June 30, 2018 and 2017 , respectively. International includes revenue from the United Kingdom of $91.5 million and $74.4 million for the three months ended June 30, 2018 and 2017 , respectively, and $174.5 million and $139.9 million for the six months ended June 30, 2018 and 2017 , respectively. There were no other individual countries that represented more than 10% of consolidated total revenue for the three and six months ended June 30, 2018 and 2017 . The following table summarizes gross profit by reportable segment and category for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 North America Service gross profit: Local $ 165,285 $ 179,609 $ 332,041 $ 348,951 Goods 2,990 3,207 6,931 4,514 Travel 16,303 17,755 32,305 32,920 Product gross profit - Goods 34,793 33,289 67,774 68,412 Total North America gross profit 219,371 233,860 439,051 454,797 International Service gross profit: Local 67,360 62,303 137,575 121,497 Goods 4,565 4,506 7,652 8,161 Travel 8,919 9,996 19,570 20,032 Product gross profit - Goods 23,443 17,402 44,695 33,031 Total International gross profit $ 104,287 $ 94,207 $ 209,492 $ 182,721 The following table summarizes operating income by reportable segment for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Operating income (loss) (1) (2) (3) (4) : North America $ (68,524 ) $ (12,033 ) $ (70,384 ) $ (26,816 ) International 4,279 4,635 9,524 7,738 Total operating income (loss) $ (64,245 ) $ (7,398 ) $ (60,860 ) $ (19,078 ) (1) Includes stock-based compensation of $15.0 million and $20.0 million for North America and $1.3 million and $1.3 million for International for the three months ended June 30, 2018 and 2017 , respectively, and $32.9 million and $38.3 million for North America and $2.7 million and $2.7 million for International for the six months ended June 30, 2018 and 2017 , respectively. (2) Includes acquisition-related (benefit) expense, net of $0.7 million for International for the three and six months ended June 30, 2018. (3) Includes restructuring charges (credits) of $0.2 million and $3.0 million for North America and $(0.6) million and $1.6 million for International for the three months ended June 30, 2018 and 2017 , respectively, and $0.2 million and $4.9 million for North America and $(0.3) million and $2.4 million for International for the six months ended June 30, 2018 and 2017 , respectively. (4) Includes a $75.0 million charge recognized in the second quarter of 2018 to increase the accrual for the IBM patent litigation matter for North America for the three and six months ended June 30, 2018 . See Note 9 , Commitments and Contingencies , for additional information. The following table summarizes the Company's total assets by reportable segment as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Total assets: North America (1) $ 871,222 $ 1,045,072 International (1) 617,478 632,433 Consolidated total assets $ 1,488,700 $ 1,677,505 (1) North America contains assets from the United States of $846.3 million and $1,006.2 million as of June 30, 2018 and December 31, 2017 , respectively. International contains assets from Ireland of $162.7 million and $219.7 million as of June 30, 2018 and December 31, 2017 , respectively. There were no other individual countries that represented more than 10% of consolidated total assets as of June 30, 2018 and December 31, 2017 .

ADOPTION OF NEW ACCOUNTING ST24

ADOPTION OF NEW ACCOUNTING STANDARDS (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. The Company's condensed consolidated financial statements were prepared in accordance with U.S. GAAP and include the assets, liabilities, revenue and expenses of all wholly-owned subsidiaries and majority-owned subsidiaries over which the Company exercises control and variable interest entities for which the Company has determined that it is the primary beneficiary. Outside stockholders' interests in subsidiaries are shown on the condensed consolidated financial statements as Noncontrolling interests. Equity investments in entities in which the Company does not have a controlling financial interest are accounted for under the equity method, the fair value option, as available-for-sale securities or at cost adjusted for observable price changes and impairments, as appropriate.
Reclassification and Terminology Changes	Reclassifications and Terminology Changes Certain reclassifications have been made to the condensed consolidated financial statements of prior periods and the accompanying notes to conform to the current period presentation, including the change in presentation of restricted cash in the condensed consolidated statements of cash flows upon adoption of ASU 2016-18. Refer to Note 2 , Adoption of New Accounting Standards , for additional information. Additionally, in prior years, the Company referred to its product revenue and service revenue as "direct revenue" and "third-party and other revenue," respectively. This terminology change did not impact the amounts presented in the condensed consolidated financial statements.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires estimates and assumptions that affect the reported amounts and classifications of assets and liabilities, revenue and expenses, and the related disclosures of contingent liabilities in the condensed consolidated financial statements and accompanying notes. Estimates are used for, but not limited to, variable consideration from unredeemed vouchers, income taxes, valuation of goodwill and intangible assets, investments, customer refunds, contingent liabilities and the useful lives of property, equipment and software and intangible assets. Actual results could differ materially from those estimates.
Adoption of New Accounting Standards	The Company adopted the guidance in ASC Topic 606, Revenue from Contracts with Customers , on January 1, 2018. Topic 606 is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods or services. See Changes to Accounting Policies from Adoption of New Accounting Standards below and Note 11 , Revenue Recognition , for information on the impact of adopting Topic 606 on the Company's accounting policies. The Company adopted the guidance in ASU 2016-01, Financial Instruments (Topic 825-10) - Recognition and Measurement of Financial Assets and Financial Liabilities , as amended, on January 1, 2018 . This ASU generally requires equity investments to be measured at fair value with changes in fair value recognized through net income and eliminates the cost method for equity securities. However, for equity investments without readily determinable fair values the ASU permits entities to elect to measure the investments at cost adjusted for observable price changes and impairments, with changes in the measurement recognized through net income. The Company applied that measurement alternative to our equity investments that were previously accounted for under the cost method. The adoption of ASU 2016-01 did not have a material impact on the condensed consolidated financial statements. See Changes to Accounting Policies from Adoption of New Accounting Standards below for additional information on the impact of adopting the ASU on the Company's accounting policies. The Company adopted the guidance in ASU 2016-18, Statement of Cash Flows (Topic 230) - Restricted Cash , on January 1, 2018. This ASU requires companies to include amounts generally described as restricted cash and restricted cash equivalents, along with cash and cash equivalents, when reconciling the beginning-of-period and end-of-period amounts shown on the statement of cash flows. Previously, changes in restricted cash were reported within cash flows from operating activities. The Company applied that change in cash flow classification on a retrospective basis, which resulted in an increase of $0.5 million to net cash used in operating activities for the six months ended June 30, 2017 . Restricted cash primarily represents amounts that the Company is unable to access for operational purposes pursuant to letters of credit with financial institutions. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets to amounts shown in the condensed consolidated statements of cash flows, as of June 30, 2018 and 2017 and December 31, 2017 (in thousands): June 30, 2018 June 30, 2017 December 31, 2017 Cash and cash equivalents $ 662,893 $ 618,550 $ 880,129 Restricted cash included in prepaid expenses and other current assets 4,250 6,569 4,932 Restricted cash included in other non-current assets 398 5,279 420 Cash, cash equivalents and restricted cash $ 667,541 $ 630,398 $ 885,481 The Company adopted the guidance in ASU 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20) - Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets , on January 1, 2018. This ASU is meant to clarify the scope of ASC Subtopic 610-20, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets , and to add guidance for partial sales of nonfinancial assets. The adoption of ASU 2017-05 did not have a material impact on the condensed consolidated financial statements. The Company adopted the guidance in ASU 2017-07, Compensation - Retirement Benefits (Topic 715) - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost , on January 1, 2018. This ASU requires employers to include only the service cost component of net periodic pension cost in operating expenses, together with other employee compensation costs. The other components of net periodic pension cost, including interest cost, expected return on plan assets, amortization of prior service cost and settlement and curtailment effects, are to be included in non-operating expenses. The adoption of ASU 2017-07 did not have a material impact on the condensed consolidated financial statements. The Company adopted the guidance in ASU 2017-09, Compensation - Stock Compensation (Topic 718) - Scope of Modification Accounting , on January 1, 2018. This ASU clarifies the changes to terms or conditions of a share-based payment award that require an entity to apply modification accounting. The adoption of ASU 2017-09 did not have a material impact on the condensed consolidated financial statements. The Company adopted the guidance in ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, as of January 1, 2018. This ASU permits a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act (the "Jobs Act"). As a result of the adoption of ASU 2018-02, the Company reclassified $0.2 million from accumulated other comprehensive income (loss) to accumulated deficit.
Revenue Recognition	Revenue Recognition Prior to its adoption of Topic 606, the Company recognized revenue when the following criteria were met: persuasive evidence of an arrangement existed; delivery had occurred; the selling price was fixed or determinable and collection was reasonably assured. Following its adoption of Topic 606, the Company recognizes revenue when it satisfies a performance obligation by transferring a promised good or service to a customer. Substantially all of the Company's performance obligations are satisfied at a point in time rather than over time. Product Revenue The Company generates product revenue from direct sales of merchandise inventory through its Goods category. For product revenue transactions, the Company is the primary party responsible for providing the good to the customer, it has inventory risk and it has discretion in establishing prices. As such, product revenue is reported on a gross basis as the purchase price received from the customer. Product revenue, including associated shipping revenue, is recognized when title passes to the customer upon delivery of the product. Service Revenue Service revenue is primarily earned from transactions in which the Company earns commissions by selling goods or services on behalf of third-party merchants. Those transactions generally involve a customer's purchase of a voucher through one of the Company's online marketplaces that can be redeemed with a third-party merchant for specified goods or services (or for discounts on specified goods or services). Service revenue from those transactions is reported on a net basis as the purchase price collected from the customer less the portion of the purchase price that is payable to the third-party merchant. The Company recognizes revenue from those transactions when its commission has been earned, which occurs when a sale through one of the Company's online marketplaces is completed and the related voucher has been made available to the customer. The Company believes that its remaining obligations to remit payment to the merchant and to provide information about vouchers sold are administrative activities that are immaterial in the context of the contract with the merchant. Prior to its adoption of Topic 606, the Company deferred the revenue from hotel reservation offerings until the customer's stay commenced. Following its adoption of Topic 606, revenue from hotel reservation offerings is recognized at the time the reservation is made, net of an allowance for estimated cancellations. The Company also earns commissions when customers make purchases with retailers using digital coupons accessed through its websites and mobile applications and from voucherless merchant offerings in which customers earn cash back on their credit card statements when they transact with third-party merchants. The Company recognizes those commissions as revenue in the period in which the underlying transactions between the customer and the third-party merchant are completed. Variable Consideration for Unredeemed Vouchers For merchant agreements with redemption payment terms, the merchant is not paid its share of the sale price for a voucher sold through one of the Company's online marketplaces until the customer redeems the related voucher. If the customer does not redeem a voucher with such merchant payment terms, the Company retains all of the gross billings for that voucher, rather than retaining only its net commission. Prior to its adoption of Topic 606, the Company recognized that variable consideration from unredeemed vouchers and derecognized the related accrued merchant payables when its legal obligation to the merchant expired, which the Company believes is shortly after the voucher expiration date in most jurisdictions. Following its adoption of Topic 606, the Company estimates the variable consideration from vouchers that will not ultimately be redeemed and recognizes that amount as revenue at the time of sale, rather than when the Company's legal obligation expires. The Company estimates variable consideration from unredeemed vouchers using its historical voucher redemption experience. If actual redemptions differ from the Company's estimates, the effects could be material to the condensed consolidated financial statements. Refunds Prior to the adoption of Topic 606, refunds were recorded as a reduction of revenue, except for refunds on service revenue transactions for which the merchant's share was not recoverable, which were presented as a cost of revenue. Following the adoption of Topic 606, all refunds are recorded as a reduction of revenue. The liability for estimated refunds is included within Accrued expenses and other current liabilities on the condensed consolidated balance sheets. The Company estimates its refund reserve using historical refund experience by deal category. The Company assesses the trends that could affect its estimates on an ongoing basis and makes adjustments to the refund reserve calculations if it appears that changes in circumstances, including changes to the Company's refund policies or general economic conditions, may cause future refunds to differ from its initial estimates. If actual refunds differ from the Company's estimates, the effects could be material to the condensed consolidated financial statements. Discounts, Customer Credits and Other Consideration Payable to Customers The Company provides discount offers to encourage purchases of goods and services through its online marketplaces. The Company records discounts as a reduction of revenue. Additionally, the Company issues credits to customers that can be applied to future purchases through its online marketplaces. Credits are primarily issued as consideration for refunds. To a lesser extent, credits are issued for customer relationship purposes. Credits issued to satisfy refund requests are applied as a reduction to the refunds reserve. Prior to the adoption of Topic 606, customer credits issued for relationship purposes were classified in the condensed consolidated statement of operations as a marketing expense. Following the adoption of Topic 606, customer credits issued for relationship purposes are classified as a reduction of revenue. Prior to its adoption of Topic 606, the Company recognized breakage income for unused customer credits when they expired or were forfeited. Following its adoption of Topic 606, breakage income from customer credits that are not expected to be used is estimated and recognized as revenue in proportion to the pattern of redemption for customer credits that are used. Sales and Related Taxes Sales, use, value-added and related taxes that are imposed on specific revenue-generating transactions are presented on a net basis and excluded from revenue. Costs of Obtaining Contracts Prior to its adoption of Topic 606, the Company expensed the incremental costs to obtain contracts with third-party merchants, such as sales commissions, as incurred. Following its adoption of Topic 606, those costs are deferred and recognized over the expected period of the merchant arrangement, generally from 12 to 18 months. As of June 30, 2018 , the Company had $3.4 million and $11.5 million of deferred contract acquisition costs recorded within Prepaid expenses and other current assets and Other non-current assets, respectively. For the three and six months ended June 30, 2018 , the Company amortized $6.5 million and $13.3 million , respectively, of deferred contract acquisition costs and did not recognize any impairment losses in relation to the deferred costs. Those costs are classified within Selling, general and administrative expenses in the condensed consolidated statements of operations.
Cost of Revenue	Cost of Revenue Cost of revenue is comprised of direct and certain indirect costs incurred to generate revenue. Costs incurred to generate revenue, which include credit card processing fees, editorial costs, compensation expense for technology support personnel who are responsible for maintaining the infrastructure of the Company's websites, amortization of internal-use software relating to customer-facing applications, web hosting and other processing fees are attributed to the cost of service and product revenue in proportion to gross billings during the period. For product revenue transactions, cost of revenue also includes the cost of inventory, shipping and fulfillment costs and inventory markdowns. Fulfillment costs are comprised of third-party logistics provider costs, as well as rent, depreciation, personnel costs and other costs of operating the Company's fulfillment center. Prior to adoption of Topic 606, cost of revenue on service revenue transactions also included refunds for which the merchant's share was not recoverable.
Financial Instruments	Prior to the adoption of the guidance in ASU 2016-01, investments in nonmarketable equity shares with no redemption provisions that are not common stock or in-substance common stock or for which the Company does not have the ability to exercise significant influence were accounted for using the cost method of accounting. Those investments are classified within Investments on the condensed consolidated balance sheets. Under the cost method of accounting, investments were carried at cost and adjusted only for other-than-temporary declines in fair value, certain distributions and additional investments. Subsequent to the adoption of the guidance in ASU 2016-01, the Company applies a measurement alternative for equity investments without readily determinable fair values that permits entities to elect to measure the investments at cost adjusted for observable price changes and impairments, with changes in the measurement recognized through net income.

ADOPTION OF NEW ACCOUNTING ST25

ADOPTION OF NEW ACCOUNTING STANDARDS (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets to amounts shown in the condensed consolidated statements of cash flows, as of June 30, 2018 and 2017 and December 31, 2017 (in thousands): June 30, 2018 June 30, 2017 December 31, 2017 Cash and cash equivalents $ 662,893 $ 618,550 $ 880,129 Restricted cash included in prepaid expenses and other current assets 4,250 6,569 4,932 Restricted cash included in other non-current assets 398 5,279 420 Cash, cash equivalents and restricted cash $ 667,541 $ 630,398 $ 885,481

DISCONTINUED OPERATIONS AND O26

DISCONTINUED OPERATIONS AND OTHER BUSINESS DISPOSITIONS (Tables)	6 Months Ended
	Jun. 30, 2018
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax [Abstract]
Schedule of Gain (Loss) on Business Dispositions	The Company recognized a net pretax loss on those dispositions of $1.3 million , which consisted of the following (in thousands): Net consideration received: Fair value of minority investments retained or acquired $ 2,021 Cash proceeds received 3,462 Cash proceeds receivable 2,000 Less: transaction costs 1,394 Total net consideration received 6,089 Cumulative translation gain reclassified to earnings 14,718 Less: Net book value upon closing of the transactions 14,596 Less: Indemnification liabilities (1) 5,365 Less: Unfavorable contract liability for transition services 2,114 Loss on dispositions $ (1,268 ) (1) See Note 9 , Commitments and Contingencies , for additional information about the indemnification liabilities.
Schedule of Major Classes of Line Items Included in Income (Loss) From Discontinued Operations	The following table summarizes the major classes of line items included in income (loss) from discontinued operations, net of tax, for the three and six months ended June 30, 2017 (in thousands): Three Months Ended June 30, 2017 (1) Six Months Ended June 30, 2017 (2) Service revenue $ — $ 12,602 Product revenue — 2,962 Service cost of revenue — (2,557 ) Product cost of revenue — (3,098 ) Marketing expense — (1,239 ) Selling, general and administrative expense (1,376 ) (11,284 ) Restructuring — (778 ) Other income, net — 3,852 Income (loss) from discontinued operations before loss on dispositions and provision for income taxes (1,376 ) 460 Loss on dispositions — (1,268 ) Provision for income taxes — (81 ) Income (loss) from discontinued operations, net of tax $ (1,376 ) $ (889 ) (1) Selling, general and administrative expenses from discontinued operations for the three months ended June 30, 2017 primarily related to increases to contingent liabilities under indemnification agreements. See Note 9, Commitments and Contingencies , for information about indemnification obligations related to discontinued operations. (2) The income (loss) from discontinued operations before loss on dispositions and provision for income taxes for the six months ended June 30, 2017 includes the results of each business through its respective disposition date.

BUSINESS COMBINATIONS (Tables)

BUSINESS COMBINATIONS (Tables)	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Summary of Fair Value of Consideration Transferred in Acquisition	On April 30, 2018, the Company acquired 80% of the outstanding shares of Cloud Savings Company, Ltd. ("Cloud Savings"), a UK-based business that operates online discount code and digital gift card platforms. The primary purpose of this acquisition was to expand digital coupon offerings in the Company's international segment. Concurrent with the acquisition, the Company entered into an agreement with the noncontrolling shareholder giving the Company the right to acquire the remaining outstanding shares of Cloud Savings for $8.9 million in December 2018. Additionally, the noncontrolling shareholder has the right to require the Company to purchase its shares in December 2018 for that same amount. The rights and obligations to acquire the remaining outstanding shares were recorded as a financing obligation at its acquisition-date fair value of $8.6 million and is classified within Accrued expenses and other current liabilities on the condensed consolidated balance sheets. The transaction also included a contingent consideration arrangement with an acquisition-date fair value of $1.6 million . The aggregate acquisition-date fair value of the consideration transferred for the Cloud Savings acquisition totaled $74.3 million , which consisted of the following (in thousands): Cash $ 64,065 Financing obligation 8,604 Contingent consideration 1,589 Total $ 74,258
Summary of Allocation of Aggregate Acquisition Price	The following table summarizes the allocation of the aggregate acquisition price of the Cloud Savings acquisition (in thousands): Cash and cash equivalents $ 6,244 Accounts receivable 5,885 Prepaid expenses and other current assets 804 Property, equipment and software 226 Goodwill 46,217 Intangible assets (1) : Merchant relationships 20,322 Trade names 2,609 Developed technology 549 Other intangible assets 687 Total assets acquired $ 83,543 Accounts payable $ 693 Accrued merchant and supplier payables 386 Accrued expenses and other current liabilities 6,130 Other non-current liabilities 2,076 Total liabilities assumed $ 9,285 Total acquisition price $ 74,258 (1) The estimated useful lives of the acquired intangible assets are 6 years for merchant relationships, 8 years for trade names, 2 years for developed technology, and 1 year for other intangible assets.

GOODWILL AND OTHER INTANGIBLE28

GOODWILL AND OTHER INTANGIBLE ASSETS (Tables)	6 Months Ended
	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The following table summarizes the Company's goodwill activity by segment for the six months ended June 30, 2018 (in thousands): North America International Consolidated Balance as of December 31, 2017 $ 178,685 $ 108,304 $ 286,989 Goodwill related to acquisition — 46,217 46,217 Foreign currency translation — (4,407 ) (4,407 ) Balance as of June 30, 2018 $ 178,685 $ 150,114 $ 328,799
Schedule of Intangible Assets	The following table summarizes the Company's intangible assets as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Asset Category Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Customer relationships $ 55,952 $ 48,695 $ 7,257 $ 56,749 $ 46,513 $ 10,236 Merchant relationships 30,969 10,778 20,191 11,598 9,853 1,745 Trade names 14,456 10,965 3,491 12,077 10,469 1,608 Developed technology 37,151 36,667 484 36,864 36,864 — Patents 20,132 15,895 4,237 19,031 15,204 3,827 Other intangible assets 11,342 9,927 1,415 10,875 9,095 1,780 Total $ 170,002 $ 132,927 $ 37,075 $ 147,194 $ 127,998 $ 19,196
Schedule of Estimated Future Amortization Expense	As of June 30, 2018 , the Company's estimated future amortization expense related to intangible assets is as follows (in thousands): Remaining amounts in 2018 $ 7,446 2019 11,025 2020 5,120 2021 4,393 2022 4,077 Thereafter 5,014 Total $ 37,075

INVESTMENTS (Tables)

INVESTMENTS (Tables)	6 Months Ended
	Jun. 30, 2018
Schedule of Equity Method Investments [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables summarize the Company's assets that are measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 (in thousands): Fair Value Measurement at Reporting Date Using June 30, 2018 Quoted Prices in Active Markets for Significant Other Significant Assets: Fair value option investments $ 74,898 $ — $ — $ 74,898 Available-for-sale securities: Convertible debt securities 10,236 — — 10,236 Redeemable preferred shares 9,961 — — 9,961 Liabilities: Contingent Consideration 1,542 — — 1,542 Fair Value Measurement at Reporting Date Using December 31, 2017 Quoted Prices in Active Markets for Significant Other Significant Cash equivalents $ 137,975 $ 137,975 $ — $ — Fair value option investments 82,966 — — 82,966 Available-for-sale securities: Convertible debt securities 11,354 — — 11,354 Redeemable preferred shares 15,431 — — 15,431
Summary of Investments	The following table summarizes the Company's investments as of June 30, 2018 and December 31, 2017 (dollars in thousands): June 30, 2018 Percent Ownership of Voting Stock December 31, 2017 Percent Ownership of Voting Stock Current (1) : Available-for-sale securities: Convertible debt securities $ 8,517 $ — Non-current (1) : Available-for-sale securities: Convertible debt securities $ 1,719 $ 11,354 Redeemable preferred shares 9,961 19% to 25% 15,431 19% to 25% Total available-for-sale securities 11,680 26,785 Fair value option investments 74,898 10% to 19% 82,966 10% to 19% Other equity investments (2) 23,028 1% to 19% 25,438 1% to 19% Total non-current investments $ 109,606 $ 135,189 Total investments $ 118,123 $ 135,189 (1) Current and non-current investments are classified within Prepaid expenses and other current assets and Investments, respectively, on the condensed consolidated balance sheets. (2) Represents equity investments without readily determinable fair values. Those investments were previously accounted for using the cost method of accounting. Under the cost method, investments were carried at cost and adjusted only for other-than-temporary declines in fair value, certain distributions and additional investments. The Company adopted the guidance in ASU 2016-01 on January 1, 2018. Under that guidance, the Company has elected to record equity investments without readily determinable fair values at cost adjusted for observable price changes and impairments. There were no adjustments for observable price changes related to these investments for the three and six months ended June 30, 2018 . See further discussion under Impairments of Investments below.
Schedule of Activity for Available For Sale Securities	The following table summarizes the amortized cost, gross unrealized gain, gross unrealized loss and fair value of the Company's available-for-sale securities as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Amortized Cost Gross Unrealized Gain Gross Unrealized Loss (1) Fair Value Available-for-sale securities: Convertible debt securities $ 10,129 $ 107 $ — $ 10,236 $ 10,205 $ 1,653 $ (504 ) $ 11,354 Redeemable preferred shares 9,961 — — 9,961 15,431 — — 15,431 Total available-for-sale securities $ 20,090 $ 107 $ — $ 20,197 $ 25,636 $ 1,653 $ (504 ) $ 26,785 (1) Gross unrealized loss is related to one security that was in a loss position for greater than 12 months as of December 31, 2017.

SUPPLEMENTAL CONSOLIDATED BAL30

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION (Tables)	6 Months Ended
	Jun. 30, 2018
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Schedule of Other Income (Expense)	The following table summarizes the Company's other income (expense), net for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Interest income $ 1,836 $ 659 $ 3,345 $ 1,261 Interest expense (5,228 ) (4,948 ) (10,721 ) (10,267 ) Gains (losses), net on changes in fair value of investments (3,035 ) (1,448 ) (8,068 ) (1,145 ) Foreign currency gains (losses), net (12,533 ) 10,826 (11,135 ) 10,877 Impairments of investments (9,189 ) — (10,044 ) — Other 1,692 789 1,651 550 Other income (expense), net $ (26,457 ) $ 5,878 $ (34,972 ) $ 1,276
Schedule of Prepaid and Other Current Assets	The following table summarizes the Company's prepaid expenses and other current assets as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Merchandise inventories $ 28,307 $ 25,528 Prepaid expenses 38,519 40,399 Income taxes receivable 9,565 10,299 Investments 8,517 — Other 19,616 17,799 Total prepaid expenses and other current assets $ 104,524 $ 94,025
Schedule of Accrued Merchant and Supplier Payables	The following table summarizes the Company's accrued merchant and supplier payables as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Accrued merchant payables $ 377,097 $ 459,662 Accrued supplier payables (1) 151,127 310,673 Total accrued merchant and supplier payables $ 528,224 $ 770,335 (1) Amounts include payables to suppliers of inventories and providers of shipping and fulfillment services.
Schedule of Accrued Expenses and Other Current Liabilities	The following table summarizes the Company's accrued expenses and other current liabilities as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Refunds reserve $ 30,355 $ 31,275 Compensation and benefits 55,827 73,096 Accrued marketing 29,297 32,912 Customer credits 18,316 28,487 Income taxes payable 12,448 9,645 Deferred revenue 21,802 29,539 Current portion of capital lease obligations 23,808 25,958 Accrued litigation and other (1) 175,666 100,284 Total accrued expenses and other current liabilities $ 367,519 $ 331,196
Schedule of Other Non-current Liabilities	The following table summarizes the Company's other non-current liabilities as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Contingent income tax liabilities $ 45,326 $ 43,699 Deferred rent 31,434 29,032 Capital lease obligations 12,990 18,500 Deferred income taxes 2,841 811 Other 10,644 10,366 Total other non-current liabilities $ 103,235 $ 102,408
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table summarizes the components of accumulated other comprehensive income (loss) as of June 30, 2018 and December 31, 2017 (in thousands): Foreign currency translation adjustments Unrealized gain (loss) on available-for-sale securities Total Balance as of December 31, 2017 $ 30,962 $ 882 $ 31,844 Reclassification for impact of U.S. tax rate change — 161 161 Other comprehensive income (loss) 1,238 (936 ) 302 Balance as of June 30, 2018 $ 32,200 $ 107 $ 32,307

FINANCING ARRANGEMENTS Schedule

FINANCING ARRANGEMENTS Schedule of Convertible Debt (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Schedule of Notes	The carrying amount of the Notes consisted of the following as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Liability component: Principal amount $ 250,000 $ 250,000 Less: debt discount (54,441 ) (60,247 ) Net carrying amount of liability component $ 195,559 $ 189,753 Net carrying amount of equity component $ 67,014 $ 67,014
Schedule of Convertible Debt Interest Expense	During the three and six months ended June 30, 2018 and 2017 , the Company recognized interest costs on the Notes as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Contractual interest (3.25% of the principal amount per annum) $ 2,032 $ 2,032 $ 4,064 $ 4,064 Amortization of debt discount 2,940 2,655 5,806 5,242 Total $ 4,972 $ 4,687 $ 9,870 $ 9,306

COMMITMENTS AND CONTINGENCIES C

COMMITMENTS AND CONTINGENCIES Commitment and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	In May 2018, the Company entered into a new office lease for one of its foreign locations. As of June 30, 2018 , the future payments under that operating lease for each of the next five years and thereafter are as follows (in thousands): Remaining amounts in 2018 $ 1,296 2019 2,592 2020 2,592 2021 2,592 2022 2,592 Thereafter 5,832 Total minimum lease payments $ 17,496
Long-term Purchase Commitment	In the first quarter 2018, the Company entered into a non-cancelable arrangement for cloud computing services. As of June 30, 2018 , future payments under that contractual obligation are as follows (in thousands): Remaining amounts in 2018 $ — 2019 3,400 2020 3,400 2021 3,400 2022 3,400 Total $ 13,600

STOCKHOLDERS' EQUITY AND COMP33

STOCKHOLDERS' EQUITY AND COMPENSATION ARRANGEMENTS Stock Plan (Tables)	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]	The Groupon, Inc. Stock Plans (the "Plans") are administered by the Compensation Committee of the Board (the "Compensation Committee"), which determines the number of awards to be issued, the corresponding vesting schedule and the exercise price for options. As of June 30, 2018 , 52,436,687 shares of common stock were available for future issuance under the Plans. The stock-based compensation expense related to stock awards issued under the Plans and acquisition-related awards are presented within the following line items of the condensed consolidated statements of operations for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Cost of revenue $ 288 $ 794 $ 684 $ 1,457 Marketing 1,763 2,230 3,557 4,032 Selling, general and administrative 14,215 18,368 31,303 35,553 Other income (expense) 52 48 100 99 Total stock-based compensation expense $ 16,318 $ 21,440 $ 35,644 $ 41,141 The Company also capitalized $2.0 million and $1.8 million of stock-based compensation for the three months ended June 30, 2018 and 2017 , respectively, and $3.7 million and $3.3 million for the six months ended June 30, 2018 and 2017 , respectively, in connection with internally-developed software. As of June 30, 2018 , $138.1 million of unrecognized compensation costs related to unvested employee stock awards are expected to be recognized over a remaining weighted-average period of 1.44 years.

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Prospective Adoption of New Accounting Pronouncements	The Company recorded a net reduction to its opening accumulated deficit of $88.9 million , which is net of a $6.7 million income tax effect, as of January 1, 2018 due to the cumulative impact of adopting Topic 606. The following table summarizes balance sheet accounts impacted by the cumulative effect of adopting Topic 606 (in thousands): Account Increase (decrease) to beginning accumulated deficit Prepaid expenses and other current assets $ (4,007 ) Other non-current assets (10,223 ) Accrued merchant and supplier payables (64,970 ) Accrued expenses and other current liabilities (13,188 ) Other non-current liabilities 3,443 Effect on beginning accumulated deficit $ (88,945 ) See Note 2 , Adoption of New Accounting Standards , for additional information about the Company's revenue recognition policies before and after the adoption of Topic 606. Impacts on Condensed Consolidated Financial Statements The following tables summarize the impacts of adopting Topic 606 on the Company's condensed consolidated financial statements as of and for the three and six months ended June 30, 2018 (in thousands): Condensed Consolidated Balance Sheet June 30, 2018 As reported Adjustments Balances without adoption of Topic 606 Total assets $ 1,488,700 $ (11,638 ) $ 1,477,062 Total liabilities 1,217,563 86,124 1,303,687 Total equity 271,137 (97,762 ) 173,375 C ondensed Consolidated Statements of Operations Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As reported Adjustments Balances without adoption of Topic 606 As reported Adjustments Balances without adoption of Topic 606 Revenue: Service revenue (1)(2) $ 295,652 $ 6,001 $ 301,653 $ 597,449 $ 4,222 $ 601,671 Product revenue 321,744 — 321,744 646,487 — 646,487 Total revenue 617,396 6,001 623,397 1,243,936 4,222 1,248,158 Cost of revenue: Service cost of revenue (3) 30,230 7,043 37,273 61,375 13,318 74,693 Product cost of revenue 263,508 — 263,508 534,018 — 534,018 Cost of revenue (3) 293,738 7,043 300,781 595,393 13,318 608,711 Gross profit 323,658 (1,042 ) 322,616 648,543 (9,096 ) 639,447 Operating expenses: Marketing (4) 94,178 2,134 96,312 193,334 3,707 197,041 Selling, general and administrative (5) 294,124 (1,227 ) 292,897 516,185 (2,491 ) 513,694 Restructuring charges (399 ) — (399 ) (116 ) — (116 ) Total operating expenses 387,903 907 388,810 709,403 1,216 710,619 Income (loss) from operations (64,245 ) (1,949 ) (66,194 ) (60,860 ) (10,312 ) (71,172 ) Other income (expense), net (26,457 ) — (26,457 ) (34,972 ) — (34,972 ) Income (loss) before provision (benefit) for income taxes (90,702 ) (1,949 ) (92,651 ) (95,832 ) (10,312 ) (106,144 ) Provision (benefit) for income taxes (6) 1,552 886 2,438 (783 ) (133 ) (916 ) Net income (loss) $ (92,254 ) $ (2,835 ) $ (95,089 ) $ (95,049 ) $ (10,179 ) $ (105,228 ) (1) For the three months ended June 30, 2018 , reflects a $9.2 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, and an increase of $0.5 million related to the timing of recognition of revenue from hotel reservation offerings, partially offset by decreases of $2.9 million related to the timing of recognition of variable consideration from unredeemed vouchers and $0.8 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used. (2) For the six months ended June 30, 2018 , reflects a $17.0 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, partially offset by decreases of $8.5 million related to the timing of recognition of variable consideration from unredeemed vouchers, $2.8 million related to the timing of recognition of revenue from hotel reservation offerings and $1.5 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used. (3) Reflects an increase for refunds on service revenue transactions for which the merchant's share is not recoverable, which are classified as a reduction of revenue under Topic 606. (4) Reflects an increase for customer credits issued for relationship purposes, which are classified as a reduction of revenue under Topic 606. (5) Reflects the amortization of deferred contract acquisition costs in excess of amounts capitalized in the current period. (6) As discussed in Note 13 , Income Taxes , for the six months ended June 30, 2018 , the Company recognized an income tax benefit of $6.4 million resulting from the impact of adopting Topic 606 on intercompany activity in certain foreign jurisdictions. That income tax benefit is not reflected in this table, which presents the direct impacts of adopting Topic 606.
Disaggregation of Revenue	Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As reported Adjustments Balances without adoption of Topic 606 As reported Adjustments Balances without adoption of Topic 606 North America Service revenue: Local $ 185,870 $ 913 $ 186,783 $ 373,281 $ 4,526 $ 377,807 Goods 3,796 95 3,891 8,670 95 8,765 Travel 19,888 678 20,566 39,972 (2,401 ) 37,571 Product revenue - Goods 170,710 — 170,710 351,597 — 351,597 Total North America revenue 380,264 1,686 381,950 773,520 2,220 775,740 International Service revenue: Local 71,425 3,946 75,371 146,003 2,500 148,503 Goods 4,967 (557 ) 4,410 8,381 (796 ) 7,585 Travel 9,706 926 10,632 21,142 298 21,440 Product revenue - Goods 151,034 — 151,034 294,890 — 294,890 Total International revenue 237,132 4,315 241,447 470,416 2,002 472,418 Consolidated Service revenue: Local 257,295 4,859 262,154 519,284 7,026 526,310 Goods 8,763 (462 ) 8,301 17,051 (701 ) 16,350 Travel 29,594 1,604 31,198 61,114 (2,103 ) 59,011 Product revenue - Goods 321,744 — 321,744 646,487 — 646,487 Total Consolidated Revenue $ 617,396 $ 6,001 $ 623,397 $ 1,243,936 $ 4,222 $ 1,248,158
Deferred Revenue, by Arrangement, Disclosure	The following table summarizes the activity in the liability for customer credits for the six months ended June 30, 2018 (in thousands): Customer Credits Balance as of January 1, 2018 $ 19,414 Credits issued 67,025 Credits redeemed (1) (57,074 ) Breakage revenue recognized (10,961 ) Foreign currency translation (88 ) Balance as of June 30, 2018 $ 18,316 (1) Customer credits can be redeemed through the Company's online marketplaces for goods or services provided by a third-party merchant or for merchandise inventory sold by the Company. When customer credits are redeemed for goods or services provided by a third-party merchant, service revenue is recognized on a net basis as the difference between the carrying amount of the customer credit liability derecognized and the amount due to the merchant for the related transaction. When customer credits are redeemed for merchandise inventory sold by the Company, product revenue is recognized on a gross basis equal to the amount of the customer credit liability derecognized. Customer credits are primarily used within one year of issuance. The following table summarizes the activity in revenue deferred from contracts with customers for the six months ended June 30, 2018 (in thousands): Deferred Revenue Balance as of January 1, 2018 $ 25,763 Revenue deferred 21,802 Revenue recognized (25,364 ) Foreign currency translation (399 ) Balance as of June 30, 2018 $ 21,802

RESTRUCTURING (Tables)

RESTRUCTURING (Tables)	6 Months Ended
	Jun. 30, 2018
Restructuring and Related Activities [Abstract]
Summary of Costs Incurred by Segment Related to Restructuring	The following tables summarize the costs incurred by segment related to the Company’s restructuring plan for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, 2018 Employee Severance and Benefit Costs (1) Other Exit Costs (1) Total Restructuring Charges (Credits) North America $ — $ 177 $ 177 International (576 ) — (576 ) Consolidated $ (576 ) $ 177 $ (399 ) Six Months Ended June 30, 2018 Employee Severance and Benefit Costs (1) Other Exit Costs (1) Total Restructuring Charges (Credits) North America $ — $ 177 $ 177 International (346 ) 53 (293 ) Consolidated $ (346 ) $ 230 $ (116 ) Three Months Ended June 30, 2017 Employee Severance and Benefit Costs (2) Other Exit Costs Total Restructuring Charges North America $ 2,687 $ 288 $ 2,975 International 86 1,523 1,609 Consolidated $ 2,773 $ 1,811 $ 4,584 Six Months Ended June 30, 2017 Employee Severance and Benefit Costs (2) Other Exit Costs Total Restructuring Charges North America $ 4,465 $ 465 $ 4,930 International 609 1,776 2,385 Consolidated $ 5,074 $ 2,241 $ 7,315 (1) The $0.4 million and $0.1 million of restructuring credits for the three and six months ended June 30, 2018 , respectively, reflect changes in estimates related to prior actions. (2) The employee severance and benefit costs for the three and six months ended June 30, 2017 related to the termination of approximately 150 and 350 employees, respectively.
Schedule of Restructuring Liability	The following table summarizes the restructuring liability activity for the six months ended June 30, 2018 (in thousands): Employee Severance and Benefit Costs Other Exit Costs Total Balance as of December 31, 2017 $ 3,817 $ 304 $ 4,121 Charges payable in cash (346 ) 230 (116 ) Cash payments (1,428 ) (53 ) (1,481 ) Foreign currency translation (67 ) — (67 ) Balance as of June 30, 2018 $ 1,976 $ 481 $ 2,457

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables summarize the Company's assets that are measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 (in thousands): Fair Value Measurement at Reporting Date Using June 30, 2018 Quoted Prices in Active Markets for Significant Other Significant Assets: Fair value option investments $ 74,898 $ — $ — $ 74,898 Available-for-sale securities: Convertible debt securities 10,236 — — 10,236 Redeemable preferred shares 9,961 — — 9,961 Liabilities: Contingent Consideration 1,542 — — 1,542 Fair Value Measurement at Reporting Date Using December 31, 2017 Quoted Prices in Active Markets for Significant Other Significant Cash equivalents $ 137,975 $ 137,975 $ — $ — Fair value option investments 82,966 — — 82,966 Available-for-sale securities: Convertible debt securities 11,354 — — 11,354 Redeemable preferred shares 15,431 — — 15,431
Fair Value, Assets and Liabilities, Reconciliation of Level 3 Inputs	The following table provides a roll-forward of the fair value of recurring Level 3 fair value measurements for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Assets Fair value option investments: Beginning Balance $ 77,933 $ 82,887 $ 82,966 $ 82,584 Total gains (losses) included in earnings (3,035 ) (1,448 ) (8,068 ) (1,145 ) Ending Balance $ 74,898 $ 81,439 $ 74,898 $ 81,439 Unrealized gains (losses) still held (1) $ (3,035 ) $ (1,448 ) $ (8,068 ) $ (1,145 ) Available-for-sale securities Convertible debt securities: Beginning Balance $ 11,070 $ 11,931 $ 11,354 $ 10,038 Purchase of convertible debt security — — — 1,612 Proceeds at maturity of convertible debt security — (1,843 ) — (1,843 ) Transfer to other equity investment upon conversion of convertible debt security (2,508 ) — (2,508 ) — Total gains (losses) included in other comprehensive income (loss) (541 ) (575 ) (1,042 ) (533 ) Total gains (losses) included in earnings (2) 2,215 1,355 2,432 1,594 Ending Balance $ 10,236 $ 10,868 $ 10,236 $ 10,868 Unrealized gains (losses) still held (1) $ 2,599 $ 512 $ 2,405 $ 816 Redeemable preferred shares: Beginning Balance $ 14,576 $ 17,788 $ 15,431 $ 17,444 Total gains (losses) included in other comprehensive income (loss) — (1,865 ) — (1,521 ) Impairments included in earnings (4,615 ) — (5,470 ) — Ending Balance $ 9,961 $ 15,923 $ 9,961 $ 15,923 Unrealized (losses) gains still held (1) $ (4,615 ) $ (1,865 ) $ (5,470 ) $ (1,521 ) Liabilities Contingent Consideration: Beginning Balance $ — $ 14,600 $ — $ 14,588 Issuance of contingent consideration in connection with acquisition 1,589 — 1,589 — Settlements of contingent consideration liabilities — (7,858 ) — (7,858 ) Reclass to non-fair value liabilities when no longer contingent — (6,778 ) — (6,778 ) Total losses (gains) included in earnings 14 36 14 48 Foreign currency translation (61 ) — (61 ) — Ending Balance $ 1,542 $ — $ 1,542 $ — Unrealized losses (gains) still held (1) $ (47 ) $ — $ (47 ) $ —
Fair Value of Financial Assets and Liabilities not Measured at Fair Value		The following table presents the carrying amount and fair value of equity securities that were classified as cost method investments as of December 31, 2017 (in thousands): December 31, 2017 Carrying Amount Fair Value Cost method investments (1) $ 25,438 $ 32,792 (1) See Note 2 , Adoption of New Accounting Standards , and Note 6 , Investments , for information about the Company's adoption of ASU 2016-01 on January 1, 2018 and its impact on accounting for equity investments without readily determinable fair values that were previously subject to the cost method of accounting.

INCOME (LOSS) PER SHARE (Tables

INCOME (LOSS) PER SHARE (Tables)	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Income (Loss) Per Share	The following table sets forth the computation of basic and diluted net income (loss) per share of common stock for the three and six months ended June 30, 2018 and 2017 (in thousands, except share amounts and per share amounts): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Basic and diluted net income (loss) per share: Numerator Net income (loss) - continuing operations $ (92,254 ) $ (5,403 ) $ (95,049 ) $ (26,272 ) Less: Net income (loss) attributable to noncontrolling interests 2,780 2,547 6,873 6,579 Net income (loss) attributable to common stockholders - continuing operations (95,034 ) (7,950 ) (101,922 ) (32,851 ) Net income (loss) attributable to common stockholders - discontinued operations — (1,376 ) — (889 ) Net income (loss) attributable to common stockholders $ (95,034 ) $ (9,326 ) $ (101,922 ) $ (33,740 ) Denominator Weighted-average common shares outstanding 565,284,705 559,762,180 563,502,954 560,978,712 Basic and diluted net income (loss) per share (1) : Continuing operations $ (0.17 ) $ (0.01 ) $ (0.18 ) $ (0.06 ) Discontinued operations 0.00 (0.01 ) 0.00 0.00 Basic and diluted net income (loss) per share $ (0.17 ) $ (0.02 ) $ (0.18 ) $ (0.06 ) (1) The potentially dilutive impacts of outstanding equity awards, warrants and convertible senior notes have been excluded from the calculation of dilutive net income (loss) per share for the three and six months ended June 30, 2018 and 2017 as their effect on net income (loss) per share from continuing operations was antidilutive.
Schedule of Weighted-Average Potentially Dilutive Instruments	The following weighted-average potentially dilutive instruments are not included in the diluted net income (loss) per share calculations above because they would have had an antidilutive effect on the net income (loss) per share from continuing operations: Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Restricted stock units 32,602,563 30,134,808 30,378,335 27,247,728 Other stock-based compensation awards 1,615,249 3,437,075 2,413,637 3,667,440 Convertible senior notes 46,296,300 46,296,300 46,296,300 46,296,300 Warrants 46,296,300 46,296,300 46,296,300 46,296,300 Total 126,810,412 126,164,483 125,384,572 123,507,768

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Schedule of Revenue by Reportable Segment	The following table summarizes revenue by reportable segment and category for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 North America Service revenue: Local $ 185,870 $ 207,534 $ 373,281 $ 408,079 Goods 3,796 4,112 8,670 5,816 Travel 19,888 22,320 39,972 42,782 Product revenue - Goods 170,710 217,946 351,597 468,592 Total North America revenue (1) 380,264 451,912 773,520 925,269 International Service revenue: Local 71,425 66,108 146,003 129,683 Goods 4,967 4,984 8,381 9,268 Travel 9,706 10,796 21,142 21,798 Product revenue - Goods 151,034 128,819 294,890 250,227 Total International revenue (1) $ 237,132 $ 210,707 $ 470,416 $ 410,976 (1) North America includes revenue from the United States of $371.1 million and $442.7 million for the three months ended June 30, 2018 and 2017 , respectively, and $756.5 million and $907.4 million for the six months ended June 30, 2018 and 2017 , respectively. International includes revenue from the United Kingdom of $91.5 million and $74.4 million for the three months ended June 30, 2018 and 2017 , respectively, and $174.5 million and $139.9 million for the six months ended June 30, 2018 and 2017 , respectively. There were no other individual countries that represented more than 10% of consolidated total revenue for the three and six months ended June 30, 2018 and 2017 .
Schedule of Gross Profit by Reportable Segment	The following table summarizes gross profit by reportable segment and category for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 North America Service gross profit: Local $ 165,285 $ 179,609 $ 332,041 $ 348,951 Goods 2,990 3,207 6,931 4,514 Travel 16,303 17,755 32,305 32,920 Product gross profit - Goods 34,793 33,289 67,774 68,412 Total North America gross profit 219,371 233,860 439,051 454,797 International Service gross profit: Local 67,360 62,303 137,575 121,497 Goods 4,565 4,506 7,652 8,161 Travel 8,919 9,996 19,570 20,032 Product gross profit - Goods 23,443 17,402 44,695 33,031 Total International gross profit $ 104,287 $ 94,207 $ 209,492 $ 182,721
Schedule of Operating Income by Reportable Segment	The following table summarizes operating income by reportable segment for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Operating income (loss) (1) (2) (3) (4) : North America $ (68,524 ) $ (12,033 ) $ (70,384 ) $ (26,816 ) International 4,279 4,635 9,524 7,738 Total operating income (loss) $ (64,245 ) $ (7,398 ) $ (60,860 ) $ (19,078 ) (1) Includes stock-based compensation of $15.0 million and $20.0 million for North America and $1.3 million and $1.3 million for International for the three months ended June 30, 2018 and 2017 , respectively, and $32.9 million and $38.3 million for North America and $2.7 million and $2.7 million for International for the six months ended June 30, 2018 and 2017 , respectively. (2) Includes acquisition-related (benefit) expense, net of $0.7 million for International for the three and six months ended June 30, 2018. (3) Includes restructuring charges (credits) of $0.2 million and $3.0 million for North America and $(0.6) million and $1.6 million for International for the three months ended June 30, 2018 and 2017 , respectively, and $0.2 million and $4.9 million for North America and $(0.3) million and $2.4 million for International for the six months ended June 30, 2018 and 2017 , respectively. (4) Includes a $75.0 million charge recognized in the second quarter of 2018 to increase the accrual for the IBM patent litigation matter for North America for the three and six months ended June 30, 2018 .
Schedule of Total Assets by Segment	The following table summarizes the Company's total assets by reportable segment as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Total assets: North America (1) $ 871,222 $ 1,045,072 International (1) 617,478 632,433 Consolidated total assets $ 1,488,700 $ 1,677,505 (1) North America contains assets from the United States of $846.3 million and $1,006.2 million as of June 30, 2018 and December 31, 2017 , respectively. International contains assets from Ireland of $162.7 million and $219.7 million as of June 30, 2018 and December 31, 2017 , respectively. There were no other individual countries that represented more than 10% of consolidated total assets as of June 30, 2018 and December 31, 2017 .

DESCRIPTION OF BUSINESS AND B39

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details)	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of segments	2

ADOPTION OF NEW ACCOUNTING ST40

ADOPTION OF NEW ACCOUNTING STANDARDS - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI, Current Period, Stranded Tax Effects ASU 2018-02, Tax		$ 161
Amortization	$ 6,500	13,300
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to net cash used in operating activities			$ 500
Other Current Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Costs	3,400	3,400
Other Noncurrent Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Costs	$ 11,500	$ 11,500

ADOPTION OF NEW ACCOUNTING ST41

ADOPTION OF NEW ACCOUNTING STANDARDS - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 662,893	$ 880,129		$ 618,550
Restricted cash included in prepaid expenses and other current assets	4,250	4,932		6,569
Restricted cash included in other non-current assets	398	420		5,279
Cash, cash equivalents and restricted cash	$ 667,541	$ 885,481	$ 630,398	$ 630,398	$ 874,906

DISCONTINUED OPERATIONS AND O42

DISCONTINUED OPERATIONS AND OTHER BUSINESS DISPOSITIONS (Details) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018		Jun. 30, 2017
Disposal Group, Including Discontinued Operation, Additional Disclosures [Abstract]
Fair value of minority investments retained or acquired						$ 0		$ 2,022
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Service revenue		$ (295,652)	[1]	$ (315,854)		(597,449)	[1]	(617,426)
Product revenue		321,744		346,765		646,487		718,819
Service cost of revenue		(30,230)	[2]	(38,478)		(61,375)	[2]	(81,351)
Product cost of revenue		(263,508)		(296,074)		(534,018)		(617,376)
Marketing expense		(94,178)	[3]	(100,658)		(193,334)	[3]	(187,000)
Selling, general and administrative expense		(294,124)	[4]	(230,223)		(516,185)	[4]	(462,281)
Restructuring		399		(4,584)		116		(7,315)
Other income, net		(26,457)		5,878		(34,972)		1,276
Income (loss) from discontinued operations, net of tax		$ 0		(1,376)		$ 0		(889)
Discontinued Operations, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Controlling stake percentage in subsidiary sold during period					83.00%
Disposal Group, Including Discontinued Operation, Additional Disclosures [Abstract]
Fair value of minority investments retained or acquired					$ 2,021
Cash proceeds received					3,462
Cash proceeds receivable					2,000
Less: transaction costs					1,394
Total net consideration received					6,089
Cumulative translation gain reclassified to earnings					14,718
Less: Net book value upon closing of the transactions					14,596
Less: Indemnification liabilities	[5]				5,365
Less: Unfavorable contract liability for transition services					2,114
Loss on dispositions				0	$ (1,268)			(1,268)
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Service revenue				0				(12,602)
Product revenue				0				2,962
Service cost of revenue				0				(2,557)
Product cost of revenue				0				(3,098)
Marketing expense				0				(1,239)
Selling, general and administrative expense				(1,376)				(11,284)
Restructuring				0				(778)
Other income, net				0				3,852
Income (loss) from discontinued operations before loss on dispositions and provision for income taxes				(1,376)				460
Provision for income taxes				$ 0				$ (81)
[1]	(1)For the three months ended June 30, 2018, reflects a $9.2 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, and an increase of $0.5 million related to the timing of recognition of revenue from hotel reservation offerings, partially offset by decreases of $2.9 million related to the timing of recognition of variable consideration from unredeemed vouchers and $0.8 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used.
[2]	Reflects an increase for refunds on service revenue transactions for which the merchant's share is not recoverable, which are classified as a reduction of revenue under Topic 606.
[3]	Reflects an increase for customer credits issued for relationship purposes, which are classified as a reduction of revenue under Topic 606.
[4]	Reflects the amortization of deferred contract acquisition costs in excess of amounts capitalized in the current period.
[5]	(1)See Note 9, Commitments and Contingencies, for additional information about the indemnification liabilities.

BUSINESS COMBINATIONS - Additio

BUSINESS COMBINATIONS - Additional Information (Details) - USD ($) $ in Thousands	Apr. 30, 2018	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition [Line Items]
Financing obligation incurred in connection with acquisition of business					$ 8,604	$ 0
Contingent consideration liability incurred in connection with acquisition of business			$ 1,589	$ 0	1,589	$ 0
External transaction costs			$ 700		$ 700
Revenue included in current period statement of operations		$ 3,000
Net loss included in current period statement of operations		$ 100
Cloud Savings
Business Acquisition [Line Items]
Percentage of outstanding shares acquired	80.00%
Gross value of financing obligation	$ 8,900
Financing obligation incurred in connection with acquisition of business	8,600
Contingent consideration liability incurred in connection with acquisition of business	1,589
Total acquisition price	$ 74,258
Merchant relationships
Business Acquisition [Line Items]
Intangible assets, useful life					6 years
Trade names
Business Acquisition [Line Items]
Intangible assets, useful life					8 years
Developed technology
Business Acquisition [Line Items]
Intangible assets, useful life					2 years
Other intangible assets
Business Acquisition [Line Items]
Intangible assets, useful life					1 year

BUSINESS COMBINATIONS - Summary

BUSINESS COMBINATIONS - Summary of Fair Value of Consideration Transferred in Acquisition (Details) - USD ($) $ in Thousands	Apr. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition [Line Items]
Financing obligation incurred in connection with acquisition of business				$ 8,604	$ 0
Contingent consideration liability incurred in connection with acquisition of business		$ 1,589	$ 0	$ 1,589	$ 0
Cloud Savings
Business Acquisition [Line Items]
Cash	$ 64,065
Financing obligation incurred in connection with acquisition of business	8,600
Contingent consideration liability incurred in connection with acquisition of business	1,589
Total acquisition price	$ 74,258

BUSINESS COMBINATIONS - Allocat

BUSINESS COMBINATIONS - Allocation of Aggregate Acquisition Price (Details) - Cloud Savings - USD ($) $ in Thousands	Apr. 30, 2018	Jun. 30, 2018
Business Acquisition [Line Items]
Cash and cash equivalents	$ 6,244
Accounts receivable	5,885
Prepaid expenses and other current assets	804
Property, equipment and software	226
Goodwill		$ 46,217
Other intangible assets	83,543
Accounts payable	693
Accrued merchant and supplier payables	386
Accrued expenses and other current liabilities	6,130
Other non-current liabilities	2,076
Total liabilities assumed	9,285
Total acquisition price	74,258
Merchant relationships
Business Acquisition [Line Items]
Intangible assets (1) :	20,322
Developed technology
Business Acquisition [Line Items]
Intangible assets (1) :	549
Other intangible assets
Business Acquisition [Line Items]
Intangible assets (1) :	687
Trade names
Business Acquisition [Line Items]
Intangible assets (1) :	$ 2,609

GOODWILL AND OTHER INTANGIBLE46

GOODWILL AND OTHER INTANGIBLE ASSETS - Schedule of Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill	$ 328,799	$ 286,989
Foreign currency translation	(4,407)
North America
Goodwill [Line Items]
Goodwill	178,685	178,685
Foreign currency translation	0
International
Goodwill [Line Items]
Goodwill	150,114	$ 108,304
Foreign currency translation	(4,407)
Cloud Savings
Goodwill [Line Items]
Goodwill related to acquisition	46,217
Cloud Savings | North America
Goodwill [Line Items]
Goodwill related to acquisition	$ 0

GOODWILL AND OTHER INTANGIBLE47

GOODWILL AND OTHER INTANGIBLE ASSETS - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 170,002	$ 147,194
Accumulated Amortization	132,927	127,998
Net Carrying Value	37,075	19,196
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	55,952	56,749
Accumulated Amortization	48,695	46,513
Net Carrying Value	7,257	10,236
Merchant relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	30,969	11,598
Accumulated Amortization	10,778	9,853
Net Carrying Value	20,191	1,745
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	14,456	12,077
Accumulated Amortization	10,965	10,469
Net Carrying Value	3,491	1,608
Developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	37,151	36,864
Accumulated Amortization	36,667	36,864
Net Carrying Value	484	0
Patents
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	20,132	19,031
Accumulated Amortization	15,895	15,204
Net Carrying Value	4,237	3,827
Other intangible assets
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	11,342	10,875
Accumulated Amortization	9,927	9,095
Net Carrying Value	$ 1,415	$ 1,780

GOODWILL AND OTHER INTANGIBLE48

GOODWILL AND OTHER INTANGIBLE ASSETS - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization of acquired intangible assets	$ 3,500	$ 6,200	$ 6,466	$ 11,583
Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life			1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life			8 years

GOODWILL AND OTHER INTANGIBLE49

GOODWILL AND OTHER INTANGIBLE ASSETS - Schedule of Estimated Future Amortization Expense (Details) $ in Thousands	Jun. 30, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Remaining amounts in 2018	$ 7,446
2,019	11,025
2,020	5,120
2,021	4,393
2,022	4,077
Thereafter	5,014
Total	$ 37,075

INVESTMENTS - Summary of Invest

INVESTMENTS - Summary of Investments (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Convertible debt securities, current		$ 8,517		$ 8,517		$ 0
Available-for-sale securities, non-current		11,680		11,680		26,785
Total non-current investments		109,606		109,606		135,189
Total Investments		118,123		118,123		135,189
Gain (loss) from changes in fair value of investments		(3,035)	$ (1,448)	(8,068)	$ (1,145)
Impairment of other equity investment		4,600		4,600
Redeemable Preferred Stock
Schedule of Equity Method Investments [Line Items]
Available-for-sale securities, non-current		9,961		9,961		15,431
Fair Value Option Investments
Schedule of Equity Method Investments [Line Items]
Equity method investments		74,898		74,898		82,966
Other Equity Investments
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	$ 23,028		$ 23,028		$ 25,438
Minimum
Schedule of Equity Method Investments [Line Items]
Available for sale securities, percent ownership of voting stock		19.00%		19.00%		19.00%
Minimum | Fair Value Option Investments
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent ownership of voting stock		10.00%		10.00%		10.00%
Minimum | Other Equity Investments
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent ownership of voting stock		1.00%		1.00%		1.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Available for sale securities, percent ownership of voting stock		25.00%		25.00%		25.00%
Maximum | Fair Value Option Investments
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent ownership of voting stock		19.00%		19.00%		19.00%
Maximum | Other Equity Investments
Schedule of Equity Method Investments [Line Items]
Equity method investment, percent ownership of voting stock		19.00%		19.00%		19.00%
Prepaid Expenses and Other Current Assets | Convertible Debt Securities
Schedule of Equity Method Investments [Line Items]
Convertible debt securities, current		$ 8,517		$ 8,517		$ 0
Investments | Convertible Debt Securities
Schedule of Equity Method Investments [Line Items]
Available-for-sale securities, non-current		1,719		1,719		11,354
Nearbuy
Schedule of Equity Method Investments [Line Items]
Equity method investments		4,300		4,300		4,000
Gain (loss) from changes in fair value of investments		19	(1,371)	217	(3,421)
Monster LP
Schedule of Equity Method Investments [Line Items]
Equity method investments		70,600		70,600		$ 78,900
Gain (loss) from changes in fair value of investments		$ (3,054)	$ (77)	$ (8,285)	$ 2,276
[1]	Represents equity investments without readily determinable fair values. Those investments were previously accounted for using the cost method of accounting. Under the cost method, investments were carried at cost and adjusted only for other-than-temporary declines in fair value, certain distributions and additional investments. The Company adopted the guidance in ASU 2016-01 on January 1, 2018. Under that guidance, the Company has elected to record equity investments without readily determinable fair values at cost adjusted for observable price changes and impairments.

INVESTMENTS - Schedule of Activ

INVESTMENTS - Schedule of Activity for Available For Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 20,090	$ 25,636
Available-for-sale securities, Gross Unrealized Gain	107	1,653
Available-for-sale securities, Gross Unrealized Loss	0	(504)
Available-for-sale securities, Fair Value	(20,197)	(26,785)
Convertible Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	10,129	10,205
Available-for-sale securities, Gross Unrealized Gain	107	1,653
Available-for-sale securities, Gross Unrealized Loss	0	(504)
Available-for-sale securities, Fair Value	(10,236)	(11,354)
Redeemable Preferred Stock
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	9,961	15,431
Available-for-sale securities, Gross Unrealized Gain	0	0
Available-for-sale securities, Gross Unrealized Loss	0	0
Available-for-sale securities, Fair Value	$ (9,961)	$ (15,431)

INVESTMENTS - Additional Inform

INVESTMENTS - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Gain (loss) from changes in fair value of investments	$ (3,035)	$ (1,448)	$ (8,068)	$ (1,145)
Other than temporary impairments of available for sale securities	4,600		5,000
Impairment of other equity investment	4,600		4,600
Monster LP
Schedule of Equity Method Investments [Line Items]
Fair value of investments	70,600		70,600		$ 78,900
Gain (loss) from changes in fair value of investments	(3,054)	(77)	(8,285)	2,276
Nearbuy
Schedule of Equity Method Investments [Line Items]
Fair value of investments	4,300		4,300		$ 4,000
Gain (loss) from changes in fair value of investments	$ 19	$ (1,371)	$ 217	$ (3,421)

SUPPLEMENTAL CONSOLIDATED BAL53

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Other Income (Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Document Fiscal Year Focus			2,018
Interest income	$ 1,836	$ 659	$ 3,345	$ 1,261
Interest expense	(5,228)	(4,948)	(10,721)	(10,267)
Gains (losses), net on changes in fair value of investments	(3,035)	(1,448)	(8,068)	(1,145)
Foreign currency gains (losses), net	(12,533)	10,826	(11,135)	10,877
Impairments of investments	(9,189)		(10,044)	0
Other	1,692	789	1,651	550
Other income (expense), net	$ (26,457)	$ 5,878	$ (34,972)	$ 1,276

SUPPLEMENTAL CONSOLIDATED BAL54

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Merchandise inventories	$ 28,307	$ 25,528
Prepaid expenses	38,519	40,399
Income taxes receivable	9,565	10,299
Investments	8,517	0
Other	19,616	17,799
Total prepaid expenses and other current assets	$ 104,524	$ 94,025

SUPPLEMENTAL CONSOLIDATED BAL55

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Accrued Merchant and Supplier Payables (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Accrued merchant payables		$ 377,097	$ 459,662
Accrued supplier payables (1)	[1]	151,127	310,673
Total accrued merchant and supplier payables		$ 528,224	$ 770,335
[1]	(1)Amounts include payables to suppliers of inventories and providers of shipping and fulfillment services.

SUPPLEMENTAL CONSOLIDATED BAL56

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Accrued Expense and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Refunds reserve	$ 30,355	$ 31,275
Compensation and benefits	55,827	73,096
Accrued marketing	29,297	32,912
Customer credits	18,316	28,487
Income taxes payable	12,448	9,645
Deferred revenue	21,802	29,539
Current portion of capital lease obligations	23,808	25,958
Accrued litigation and other (1)	175,666	100,284
Total accrued expenses and other current liabilities	$ 367,519	$ 331,196

SUPPLEMENTAL CONSOLIDATED BAL57

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Other Non-current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Supplemental Consolidated Balance Sheet & Statement of Operations Information [Abstract]
Contingent income tax liabilities	$ 45,326	$ 43,699
Deferred rent	31,434	29,032
Capital lease obligations	12,990	18,500
Deferred income taxes	2,841	811
Other	10,644	10,366
Total other non-current liabilities	$ 103,235	$ 102,408

SUPPLEMENTAL CONSOLIDATED BAL58

SUPPLEMENTAL CONSOLIDATED BALANCE SHEETS AND STATEMENTS OF OPERATIONS INFORMATION - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification for impact of U.S. tax rate change			$ 161
Other comprehensive income (loss)	$ 2,371	$ (8,437)	302	$ (7,183)
Accumulated other comprehensive income (loss)	32,307		32,307		$ 31,844
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign currency translation adjustments, beginning balance			30,962
Reclassification for impact of U.S. tax rate change			0
Other comprehensive income (loss)			1,238
Foreign currency translation adjustments, ending balance	32,200		32,200
Unrealized gain (loss) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss)			(936)
Unrealized gain (loss) on available-for-sale securities, beginning balance			882
Unrealized gain (loss) on available-for-sale securities, ending balance	107		107
Total Groupon, Inc. Stockholders' Equity
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss)			302
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	$ 32,307		$ 32,307		$ 31,844

FINANCING ARRANGEMENTS - Schedu

FINANCING ARRANGEMENTS - Schedule of Notes (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal amount	$ 250,000	$ 250,000
Less: debt discount	(54,441)	(60,247)
Net carrying amount of liability component	195,559	$ 189,753
Additional Paid-In Capital
Debt Instrument [Line Items]
Net carrying amount of equity component	$ 67,014

FINANCING ARRANGEMENTS - Sche60

FINANCING ARRANGEMENTS - Schedule of Convertible Debt Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Debt Disclosure [Abstract]
Contractual interest (3.25% of the principal amount per annum)	$ 2,032	$ 2,032	$ 4,064	$ 4,064
Amortization of debt discount	2,940	2,655	5,806	5,242
Total	$ 4,972	$ 4,687	$ 9,870	$ 9,306

FINANCING ARRANGEMENTS - Conver

FINANCING ARRANGEMENTS - Convertible Senior Notes (Details)	Apr. 04, 2016USD ($)$ / sharesshares	Apr. 20, 2020	Mar. 31, 2016USD ($)	Jun. 30, 2018USD ($)$ / shares	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Net proceeds					$ 243,200,000
Stated interest rate	3.25%
Principal amount converted initially	$ 1,000
Number of shares converted (in shares) | shares	185.1852
Conversion price (in usd per share) | $ / shares	$ 5.40
Common stock, par value (in usd per share) | $ / shares				$ 4.30
Closing price of stock, trigger price (in usd per share)	150.00%
Effective interest rate					9.75%
Debt related commitment fees and issuance costs					$ 6,800,000
Debt issuance costs					4,800,000
Equity component of convertible debt			$ 2,000,000
Estimated fair value of convertible notes				$ 273,800,000	$ 285,600,000
Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount of convertible senior notes	$ 250,000,000
Remaining term of notes				3 years 9 months
Subsequent Event
Debt Instrument [Line Items]
Number of threshold trading days		20
Consecutive trading days		30

FINANCING ARRANGEMENTS - Note H

FINANCING ARRANGEMENTS - Note Hedges and Warrants (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	May 09, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Disclosure [Abstract]
Cost of convertible note hedges		$ 59.1
Number of shares available to be purchased (in shares)	46.3
Strike price (in usd per share)	$ 5.40
Cash proceeds from issuance of warrants				$ 35.5
Incremental common shares attributable to dilutive effect			46.3
Exercise price (in usd per share)			$ 8.50		$ 8.50

FINANCING ARRANGEMENTS - Revolv

FINANCING ARRANGEMENTS - Revolving Credit Facility (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2016	Apr. 04, 2016
Debt Instrument [Line Items]
Aggregate principal amount	$ 250
Stated interest rate				3.25%
Unrestricted cash covenant amount			$ 400
Amount of accounts held with lenders			$ 200
Outstanding amount of lines of credit	$ 18.6	$ 22.7
Minimum
Debt Instrument [Line Items]
Unused commitment fee percentage	0.25%
Maximum
Debt Instrument [Line Items]
Unused commitment fee percentage	0.40%
Letter of Credit
Debt Instrument [Line Items]
Aggregate principal amount	$ 45
Letter of Credit | Base Rate | Minimum
Debt Instrument [Line Items]
Stated interest rate	0.50%
Letter of Credit | Base Rate | Maximum
Debt Instrument [Line Items]
Stated interest rate	2.25%
Geographic Distribution, Domestic
Debt Instrument [Line Items]
Outstanding stock percentage	100.00%
Geographic Distribution, Foreign
Debt Instrument [Line Items]
Outstanding stock percentage	65.00%

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Schedule of Future Minimum Rental Payments and Long-term Purchase Commitment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017	Mar. 09, 2017
Leases [Abstract]
Remaining amounts in 2018	$ 1,296
2,019	2,592
2,020	2,592
2,021	2,592
2,022	2,592
Thereafter	5,832
Total minimum lease payments	17,496
Other Contractual Commitments [Abstract]
Remaining amounts in 2018	0
2,019	3,400
2,020	3,400
2,021	3,400
2,022	3,400
Total	$ 13,600
Maximum exposure of indemnification liability		$ 18,000
Groupon Latin America
Other Contractual Commitments [Abstract]
Estimated indemnification liability			$ 5,400

COMMITMENTS AND CONTINGENCIES65

COMMITMENTS AND CONTINGENCIES - Additional Information (Details) - IBM Lawsuit $ in Millions	Jul. 27, 2018USD ($)	Sep. 06, 2017	May 18, 2017	May 09, 2016	Jun. 30, 2018USD ($)	Jun. 30, 2018USD ($)
Loss Contingencies [Line Items]
Provision for loss contingency					$ 75	$ 75
Number of patents allegedly infringed upon		1	2	1
Subsequent Event
Loss Contingencies [Line Items]
Awarded damages	$ 82.5
Unexpired patents infringed upon	2

STOCKHOLDERS' EQUITY AND COMP66

STOCKHOLDERS' EQUITY AND COMPENSATION ARRANGEMENTS Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Mar. 31, 2018	Feb. 13, 2018	Mar. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Available-for-sale Securities		$ 20,197		$ 20,197		$ 26,785
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		$ 1,542	$ 0	$ 1,542	$ 0	$ 0	$ 0		$ 14,600	$ 14,588
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options		217,837		217,837		885,580
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price		$ 1.81		$ 1.81		$ 0.62
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term		1 year 10 months 17 days				1 year 9 months 3 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value		$ 542		$ 542		$ 3,967
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value				$ 4.89	$ 3.78
Stock-based compensation		16,318	21,440	$ 35,644	$ 41,141
Stock Issued During Period, Shares, Employee Stock Purchase Plans					877,845
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized				7,706,474
Stock Issued During Period, Shares, Issued for Services				278,635
Common Stock, No Par Value								$ 5.20
Performance Share Units, Total Grant Date Fair Value, Conditions Met		$ 16,600		$ 16,600
Deferred Compensation Arrangement with Individual, Shares Issued				1,240,379
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number				(667,743)
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price				$ 0.10
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares		0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price				$ 0
Fair Value, Measurement with Unobservable Inputs, Unrealized Gain Loss	[1]	$ (47)	0	$ (47)	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		2,010,000,000		2,010,000,000
Preferred Stock, Capital Shares Reserved for Future Issuance		50,000,000		50,000,000
Preferred Stock, Shares Outstanding		0		0		0
Stock Repurchase Program, Authorized Amount		$ 300,000		$ 300,000
Payments for Repurchase of Common Stock				$ 0	51,513
Common Stock, Capital Shares Reserved for Future Issuance		52,436,687		52,436,687
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost		$ 2,000	1,800	$ 3,700	3,300
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized		138,100		$ 138,100
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition				1 year 5 months 8 days
Carrying Amount	[2]					$ 25,438
Cost of Sales
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation			794		1,457
Selling and Marketing Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		1,763	2,230	$ 3,557	4,032
Selling, General and Administrative Expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		14,215	18,368	31,303	35,553
Other Income
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		52	$ 48	100	$ 99
Cost of Sales
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation		288		684
Convertible Debt Securities | Fair Value, Measurements, Recurring
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Available-for-sale Securities		10,236		10,236		11,354
Convertible Debt Securities | Fair Value, Measurements, Recurring | Level 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Available-for-sale Securities		0		0		0
Convertible Debt Securities | Fair Value, Measurements, Recurring | Level 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Available-for-sale Securities		0		0		0
Redeemable Preferred Stock | Fair Value, Measurements, Recurring
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Available-for-sale Securities		9,961		9,961		15,431
Redeemable Preferred Stock | Fair Value, Measurements, Recurring | Level 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Available-for-sale Securities		0		0		0
Redeemable Preferred Stock | Fair Value, Measurements, Recurring | Level 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Available-for-sale Securities		$ 0		$ 0		$ 0
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Ownership Plan (ESOP), Number of Allocated Shares		32,860,835		32,860,835		28,939,110
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value		$ 4.51		$ 4.51		$ 4.32
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross				14,631,563
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value				$ 4.76
Vesting of restricted stock units and performance share units (in shares)				7,507,084
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value				$ 4.41
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period				(3,202,754)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Weighted Average Grant Date Fair Value				$ 4.26
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		10,000,000		10,000,000
Minimum | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period				1 year
Minimum | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period				3 years
Maximum | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period				4 years
Maximum | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period				4 years
[1]	(1)Represents the unrealized gains or losses recorded in earnings and/or other comprehensive income (loss) during the period for assets and liabilities classified as Level 3 that are still held (or outstanding) at the end of the period.
[2]	(1)See Note 2, Adoption of New Accounting Standards, and Note 6, Investments, for information about the Company's adoption of ASU 2016-01 on January 1, 2018 and its impact on accounting for equity investments without readily determinable fair values that were previously subject to the cost method of accounting.

REVENUE RECOGNITION - Additiona

REVENUE RECOGNITION - Additional Information (Details)	6 Months Ended
	Jun. 30, 2018number_of_day
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with customer, billing cycle	30
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with customer, billing cycle	150

REVENUE RECOGNITION - Impact of

REVENUE RECOGNITION - Impact of Topic 606 on Condensed Consolidated Financial Statements (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		$ 295,652	[1]	$ 315,854	$ 597,449	[1]	$ 617,426
Sales Revenue, Goods, Net		321,744		346,765	646,487		718,819
Revenue, Net		617,396	[2]	662,619	1,243,936	[2]	1,336,245
Cost of Services		30,230	[3]	38,478	61,375	[3]	81,351
Cost of Goods Sold		263,508		296,074	534,018		617,376
Cost of Revenue		293,738	[3]	334,552	595,393	[3]	698,727
Gross Profit		323,658		328,067	648,543		637,518
Marketing Expense		94,178	[4]	100,658	193,334	[4]	187,000
Selling, general and administrative		294,124	[5]	230,223	516,185	[5]	462,281
Restructuring charges (credits)		(399)		4,584	(116)		7,315
Operating Expenses		387,903		335,465	709,403		656,596
Operating Income (Loss)	[6],[7]	(64,245)		(7,398)	(60,860)		(19,078)
Other Nonoperating Income (Expense)		(26,457)		5,878	(34,972)		1,276
Income (loss) from continuing operations		(90,702)		(1,520)	(95,832)		(17,802)
Income Tax Expense (Benefit)		1,552		3,883	(783)		8,470
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		(92,254)		(6,779)	(95,049)		(27,161)
Revenue recognized from unredeemed vouchers		2,900			8,500
Hotel reservation offering revenues		500			2,800
Breakage revenue		800			1,500
Increase related to refunds on service revenue transactions		9,200			17,000
Cumulative effect of change in accounting principle, net of tax					88,945
Assets	[8]	(1,488,700)			(1,488,700)			$ (1,677,505)
Deferred Revenue		21,802			21,802			25,763
Deferred Revenue, Additions		21,802
Deferred Revenue, Revenue Recognized		(25,364)
Foreign Currency Translation, Deferred Revenue		(399)
Liabilities		1,217,563			1,217,563			1,425,660
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		271,137			271,137			251,845
International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Net	[2]	237,132		210,707	470,416		410,976
Gross Profit		104,287		94,207	209,492		182,721
Restructuring charges (credits)		(576)		1,609	(293)		2,385
Operating Income (Loss)	[6],[7]	4,279		4,635	9,524		7,738
Assets	[8]	(617,478)			(617,478)			(632,433)
North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Net	[2]	380,264		451,912	773,520		925,269
Gross Profit		219,371		233,860	439,051		454,797
Restructuring charges (credits)		177		2,975	177		4,930
Operating Income (Loss)	[6],[7]	(68,524)		(12,033)	(70,384)		(26,816)
Assets	[8]	(871,222)			(871,222)			(1,045,072)
Local
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		257,295			519,284
Local | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		71,425		66,108	146,003		129,683
Local | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		185,870		207,534	373,281		408,079
Goods
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		8,763			17,051
Sales Revenue, Goods, Net		321,744			646,487
Goods | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		4,967		4,984	8,381		9,268
Sales Revenue, Goods, Net		151,034		128,819	294,890		250,227
Goods | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		3,796		4,112	8,670		5,816
Sales Revenue, Goods, Net		170,710		217,946	351,597		468,592
Travel
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		29,594			61,114
Travel | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		9,706		10,796	21,142		21,798
Travel | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		19,888		$ 22,320	39,972		$ 42,782
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		301,653			601,671
Sales Revenue, Goods, Net		321,744			646,487
Revenue, Net	[2]	623,397			1,248,158
Cost of Services		37,273			74,693
Cost of Goods Sold		263,508			534,018
Cost of Revenue		300,781			608,711
Gross Profit		322,616			639,447
Marketing Expense		96,312			197,041
Selling, general and administrative		292,897			513,694
Restructuring charges (credits)		(399)			(116)
Operating Expenses		388,810			710,619
Operating Income (Loss)		(66,194)			(71,172)
Other Nonoperating Income (Expense)		(26,457)			(34,972)
Income (loss) from continuing operations		(92,651)			(106,144)
Income Tax Expense (Benefit)		2,438			(916)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		(95,089)			(105,228)
Assets		(1,477,062)			(1,477,062)
Liabilities		1,303,687			1,303,687
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		173,375			173,375
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Net	[2]	241,447			472,418
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Net	[2]	381,950			775,740
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Local
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		262,154			526,310
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Local | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		75,371			148,503
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Local | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		186,783			377,807
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Goods
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		8,301			16,350
Sales Revenue, Goods, Net		321,744			646,487
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Goods | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		4,410			7,585
Sales Revenue, Goods, Net		151,034			294,890
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Goods | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		3,891			8,765
Sales Revenue, Goods, Net		170,710			351,597
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Travel
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		31,198			59,011
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Travel | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		10,632			21,440
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Travel | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		20,566			37,571
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		6,001			4,222
Sales Revenue, Goods, Net		0			0
Revenue, Net	[2]	6,001			4,222
Cost of Services		7,043			13,318
Cost of Goods Sold		0			0
Cost of Revenue		7,043			13,318
Gross Profit		(1,042)			(9,096)
Marketing Expense		2,134			3,707
Selling, general and administrative		(1,227)			(2,491)
Restructuring charges (credits)		0			0
Operating Expenses		907			1,216
Operating Income (Loss)		(1,949)			(10,312)
Other Nonoperating Income (Expense)		0			0
Income (loss) from continuing operations		(1,949)			(10,312)
Income Tax Expense (Benefit)		886			(133)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		(2,835)			(10,179)
Assets		(11,638)			(11,638)
Liabilities		86,124			86,124
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		(97,762)			(97,762)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Net	[2]	4,315			2,002
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Net	[2]	1,686			2,220
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Local
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		4,859			7,026
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Local | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		3,946			2,500
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Local | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		913			4,526
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Goods
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		(462)			(701)
Sales Revenue, Goods, Net		0			0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Goods | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		(557)			(796)
Sales Revenue, Goods, Net		0			0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Goods | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		95			95
Sales Revenue, Goods, Net		0			0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Travel
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		1,604			(2,103)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Travel | International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		926			298
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Travel | North America
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Sales Revenue, Services, Net		678			(2,401)
Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax					88,945
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		270,332			270,332			$ 250,973
Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Income Tax Expense (Benefit)		$ 6,400			6,400
Accounting Standards Update 2014-09 | Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax					(88,945)
Cumulative Effect on Retained Earnings, Tax					6,700
Accounting Standards Update 2014-09 | Prepaid expenses and other current assets | Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax					(4,007)
Accounting Standards Update 2014-09 | Other non-current assets | Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax					(10,223)
Accounting Standards Update 2014-09 | Accrued merchant and supplier payables | Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax					(64,970)
Accounting Standards Update 2014-09 | Accrued expenses and other current liabilities | Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax					(13,188)
Accounting Standards Update 2014-09 | Other non-current liabilities | Total Groupon, Inc. Stockholders' Equity
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of change in accounting principle, net of tax					$ 3,443
[1]	(1)For the three months ended June 30, 2018, reflects a $9.2 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, and an increase of $0.5 million related to the timing of recognition of revenue from hotel reservation offerings, partially offset by decreases of $2.9 million related to the timing of recognition of variable consideration from unredeemed vouchers and $0.8 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used.
[2]	(1)North America includes revenue from the United States of $371.1 million and $442.7 million for the three months ended June 30, 2018 and 2017, respectively, and $756.5 million and $907.4 million for the six months ended June 30, 2018 and 2017, respectively. International includes revenue from the United Kingdom of $91.5 million and $74.4 million for the three months ended June 30, 2018 and 2017, respectively, and $174.5 million and $139.9 million for the six months ended June 30, 2018 and 2017, respectively. There were no other individual countries that represented more than 10% of consolidated total revenue for the three and six months ended June 30, 2018 and 2017.
[3]	Reflects an increase for refunds on service revenue transactions for which the merchant's share is not recoverable, which are classified as a reduction of revenue under Topic 606.
[4]	Reflects an increase for customer credits issued for relationship purposes, which are classified as a reduction of revenue under Topic 606.
[5]	Reflects the amortization of deferred contract acquisition costs in excess of amounts capitalized in the current period.
[6]	(1)Includes stock-based compensation of $15.0 million and $20.0 million for North America and $1.3 million and $1.3 million for International for the three months ended June 30, 2018 and 2017, respectively, and
[7]	Includes restructuring charges (credits) of $0.2 million and $3.0 million for North America and $(0.6) million and $1.6 million for International for the three months ended June 30, 2018 and 2017, respectively
[8]	(1)North America contains assets from the United States of $846.3 million and $1,006.2 million as of June 30, 2018 and December 31, 2017, respectively. International contains assets from Ireland of $162.7 million and $219.7 million as of June 30, 2018 and December 31, 2017, respectively. There were no other individual countries that represented more than 10% of consolidated total assets as of June 30, 2018 and December 31, 2017.

REVENUE RECOGNITION - Liability

REVENUE RECOGNITION - Liability for Customer Credits Rollforward (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Movement in Customer Refundable Fees [Roll Forward]
Balance as of January 1, 2018	$ 19,414
Credits issued	67,025
Credits redeemed	(57,074)
Breakage revenue recognized	(10,961)
Foreign currency translation	(88)
Balance as of June 30, 2018	$ 18,316

RESTRUCTURING - Summary of Cost

RESTRUCTURING - Summary of Costs Incurred by Segment Related to Restructuring (Details) $ in Thousands		3 Months Ended		6 Months Ended		31 Months Ended
		Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)numberofemployees	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)numberofemployees	Mar. 31, 2018USD ($)	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)		$ (399)	$ 4,584	$ (116)	$ 7,315
Number of employees terminated | numberofemployees			150		350
Employee Severance and Benefit Costs
Restructuring Cost and Reserve [Line Items]
Cumulative incurred costs						$ 80,100
Restructuring charges (credits)	[1]	(576)	$ 2,773	(346)	$ 5,074
Asset Impairments Related to Restructuring
Restructuring Cost and Reserve [Line Items]
Cumulative incurred costs						$ 7,500
Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)		177	1,811	230	2,241
North America
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)		177	2,975	177	4,930
North America | Employee Severance and Benefit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)	[1]	0	2,687	0	4,465
North America | Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)		177	288	177	465
International
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)		(576)	1,609	(293)	2,385
International | Employee Severance and Benefit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)	[1]	(576)	86	(346)	609
International | Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)		$ 0	$ 1,523	$ 53	$ 1,776
Facility Closing | International
Restructuring Cost and Reserve [Line Items]
Number of countries in which operations were ceased within							17
[1]	(1)

RESTRUCTURING - Schedule of Res

RESTRUCTURING - Schedule of Restructuring Liability (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Restructuring Liability Rollforward [Roll Forward]
Restructuring reserve, beginning balance	$ 4,121
Charges payable in cash	(116)
Cash payments	(1,481)
Foreign currency translation	(67)
Restructuring reserve, ending balance	2,457
Employee Severance and Benefit Costs
Restructuring Liability Rollforward [Roll Forward]
Restructuring reserve, beginning balance	3,817
Charges payable in cash	(346)
Cash payments	(1,428)
Foreign currency translation	(67)
Restructuring reserve, ending balance	1,976
Other Exit Costs
Restructuring Liability Rollforward [Roll Forward]
Restructuring reserve, beginning balance	304
Charges payable in cash	230
Cash payments	(53)
Foreign currency translation	0
Restructuring reserve, ending balance	$ 481

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Income Tax Expense (Benefit)	$ 1,552	$ 3,883	$ (783)	$ 8,470
Income (loss) from continuing operations	(90,702)	$ (1,520)	(95,832)	$ (17,802)
Accounting Standards Update 2014-09
Operating Loss Carryforwards [Line Items]
Income Tax Expense (Benefit)	6,400		6,400
International
Operating Loss Carryforwards [Line Items]
Proposed income tax assessment penalties					$ 134,500
Decrease in unrecognized benefits	$ 40,600		$ 40,600

FAIR VALUE MEASUREMENTS - Addit

FAIR VALUE MEASUREMENTS - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Apr. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	$ 1,542		$ 1,542	$ 2,600
Impairment of other equity investment	$ 4,600		$ 4,600
Monster LP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	21.00%	22.00%

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Apr. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value option investments	$ 74,898		$ 77,933	$ 82,966	$ 81,439	$ 82,887	$ 82,584
Available-for-sale Securities	20,197			26,785
Contingent consideration	1,542	$ 2,600
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets:				137,975
Fair value option investments	74,898			82,966
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets:				137,975
Contingent consideration	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets:				0
Contingent consideration	0
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets:				0
Fair value option investments	74,898			82,966
Contingent consideration	1,542
Convertible Debt Securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	10,236			11,354
Convertible Debt Securities | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0			0
Convertible Debt Securities | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0			0
Convertible Debt Securities | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	10,236			11,354
Redeemable Preferred Stock | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	9,961			15,431
Redeemable Preferred Stock | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0			0
Redeemable Preferred Stock | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0			0
Redeemable Preferred Stock | Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	$ 9,961			$ 15,431

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value, Assets and Liabilities, Reconciliation of Level 3 Inputs (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value option investments		$ 74,898	$ 81,439		$ 74,898	$ 81,439		$ 77,933	$ 82,966	$ 82,887	$ 82,584
Gain (loss) from changes in fair value of investments		(3,035)	(1,448)		(8,068)	(1,145)
Unrealized Gains (Losses) Still Held - Assets	[1]	(3,035)	(1,448)		(8,068)	(1,145)
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		1,542	0		1,542	0		0	0	14,600	14,588
Contingent consideration liability incurred in connection with acquisition of business		1,589	0		1,589	0
Business Combination, Contingent Consideration, Liability		0	(7,858)		0	(7,858)
Reclassification of contingent liability to non-fair value		0	(6,778)		0	(6,778)
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, Low		(61)		$ 0	(61)		$ 0
Purchases of Convertible Debt			0			1,612
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities		4,600			5,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[2]	14	36		14	48
Fair Value, Measurement with Unobservable Inputs, Unrealized Gain Loss	[1]	(47)	0		(47)	0
Redeemable Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value option investments		9,961	15,923		9,961	15,923		14,576	15,431	17,788	17,444
Unrealized Gains (Losses) Still Held - Assets	[1]	(4,615)	(1,865)		(5,470)	(1,521)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		0	(1,865)		0	(1,521)
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities		4,615	0		5,000	0
Convertible Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value option investments		10,236	10,868		10,236	10,868		$ 11,070	$ 11,354	$ 11,931	$ 10,038
Unrealized Gains (Losses) Still Held - Assets	[1]	2,599	512		2,405	816
Proceeds from Convertible Debt		0	(1,843)		0	(1,843)
available-for-sale investment transfer to other equity investment		(2,508)	0		(2,508)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)		(541)	(575)		(1,042)	(533)
Unrealized Gain (Loss) on Securities		2,215	$ 1,355		2,432	$ 1,594
Convertible Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payments to Acquire Investments		$ 0			$ 0
[1]	(1)Represents the unrealized gains or losses recorded in earnings and/or other comprehensive income (loss) during the period for assets and liabilities classified as Level 3 that are still held (or outstanding) at the end of the period.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjE4MjA5MGNhN2Y5OTRmNDU4YmVmN2JmOWJhOTVjMTg2fFRleHRTZWxlY3Rpb246REFFMEFDNzkwMTQyNTU5Q0I0QkIzM0M3M0FEQUNGQzcM}

FAIR VALUE MEASUREMENTS - Fai76

FAIR VALUE MEASUREMENTS - Fair Value of Financial Assets and Liabilities Not Measured at Fair Value (Details) $ in Thousands	Dec. 31, 2017USD ($)	[1]
Fair Value Disclosures [Abstract]
Carrying Amount	$ 25,438
Fair Value	$ 32,792
[1]	(1)See Note 2, Adoption of New Accounting Standards, and Note 6, Investments, for information about the Company's adoption of ASU 2016-01 on January 1, 2018 and its impact on accounting for equity investments without readily determinable fair values that were previously subject to the cost method of accounting.

INCOME (LOSS) PER SHARE - Sched

INCOME (LOSS) PER SHARE - Schedule of Computation of Basic and Diluted Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator
Net income (loss) - continuing operations	$ (92,254)	$ (5,403)	$ (95,049)	$ (26,272)
Less: Net income (loss) attributable to noncontrolling interests	2,780	2,547	6,873	6,579
Net income (loss) attributable to common stockholders - continuing operations	(95,034)	(7,950)	(101,922)	(32,851)
Income (loss) from discontinued operations, net of tax	0	(1,376)	0	(889)
Net income (loss) attributable to common stockholders	$ (95,034)	$ (9,326)	$ (101,922)	$ (33,740)
Basic And Diluted Net Income (Loss) Per Share, Denominator [Abstract]
Weighted-average common shares outstanding (in shares)	565,284,705	559,762,180	563,502,954	560,978,712
Continuing operations (in usd per share)	$ (0.17)	$ (0.01)	$ (0.18)	$ (0.06)
Discontinued operations (in usd per share)	0	(0.01)	0	0
Basic and diluted net income (loss) per share (in usd per share)	$ (0.17)	$ (0.02)	$ (0.18)	$ (0.06)

INCOME (LOSS) PER SHARE - Sch78

INCOME (LOSS) PER SHARE - Schedule of Weighted-Average Potentially Dilutive Instruments (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	126,810,412	126,164,483	125,384,572	123,507,768
Performance Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares issuable upon vesting of outstanding performance share units (in shares)	7,706,474	2,505,346
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	32,602,563	30,134,808	30,378,335	27,247,728
Other stock-based compensation awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,615,249	3,437,075	2,413,637	3,667,440
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	46,296,300	46,296,300	46,296,300	46,296,300
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	46,296,300	46,296,300	46,296,300	46,296,300

SEGMENT INFORMATION Schedule of

SEGMENT INFORMATION Schedule of Revenue by Segment (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017
Schedule of Revenue by Segment [Line Items]
Service revenue		$ 295,652	[1]	$ 315,854	$ 597,449	[1]	$ 617,426
Product revenue		321,744		346,765	646,487		718,819
Total revenue		617,396	[2]	662,619	1,243,936	[2]	1,336,245
North America
Schedule of Revenue by Segment [Line Items]
Total revenue	[2]	380,264		451,912	773,520		925,269
International
Schedule of Revenue by Segment [Line Items]
Total revenue	[2]	237,132		210,707	470,416		410,976
Local
Schedule of Revenue by Segment [Line Items]
Service revenue		257,295			519,284
Local | North America
Schedule of Revenue by Segment [Line Items]
Service revenue		185,870		207,534	373,281		408,079
Local | International
Schedule of Revenue by Segment [Line Items]
Service revenue		71,425		66,108	146,003		129,683
Goods
Schedule of Revenue by Segment [Line Items]
Service revenue		8,763			17,051
Product revenue		321,744			646,487
Goods | North America
Schedule of Revenue by Segment [Line Items]
Service revenue		3,796		4,112	8,670		5,816
Product revenue		170,710		217,946	351,597		468,592
Goods | International
Schedule of Revenue by Segment [Line Items]
Service revenue		4,967		4,984	8,381		9,268
Product revenue		151,034		128,819	294,890		250,227
Travel
Schedule of Revenue by Segment [Line Items]
Service revenue		29,594			61,114
Travel | North America
Schedule of Revenue by Segment [Line Items]
Service revenue		19,888		22,320	39,972		42,782
Travel | International
Schedule of Revenue by Segment [Line Items]
Service revenue		9,706		10,796	21,142		21,798
UNITED STATES
Schedule of Revenue by Segment [Line Items]
Revenues		371,100		442,700	756,500		907,400
UNITED KINGDOM
Schedule of Revenue by Segment [Line Items]
Revenues		$ 91,500		$ 74,400	$ 174,500		$ 139,900
[1]	(1)For the three months ended June 30, 2018, reflects a $9.2 million increase for refunds on service revenue transactions for which the merchant's share is not recoverable and customer credits issued for relationship purposes, which are classified as reductions of revenue under Topic 606, and an increase of $0.5 million related to the timing of recognition of revenue from hotel reservation offerings, partially offset by decreases of $2.9 million related to the timing of recognition of variable consideration from unredeemed vouchers and $0.8 million related to the timing of recognition of breakage revenue from customer credits that are not expected to be used.
[2]	(1)North America includes revenue from the United States of $371.1 million and $442.7 million for the three months ended June 30, 2018 and 2017, respectively, and $756.5 million and $907.4 million for the six months ended June 30, 2018 and 2017, respectively. International includes revenue from the United Kingdom of $91.5 million and $74.4 million for the three months ended June 30, 2018 and 2017, respectively, and $174.5 million and $139.9 million for the six months ended June 30, 2018 and 2017, respectively. There were no other individual countries that represented more than 10% of consolidated total revenue for the three and six months ended June 30, 2018 and 2017.

SEGMENT INFORMATION Schedule 80

SEGMENT INFORMATION Schedule of Gross Profit by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Gross Profit	$ 323,658	$ 328,067	$ 648,543	$ 637,518
North America
Segment Reporting Information [Line Items]
Gross Profit	219,371	233,860	439,051	454,797
International
Segment Reporting Information [Line Items]
Gross Profit	104,287	94,207	209,492	182,721
Service | Local | North America
Segment Reporting Information [Line Items]
Gross Profit	165,285	179,609	332,041	348,951
Service | Local | International
Segment Reporting Information [Line Items]
Gross Profit	67,360	62,303	137,575	121,497
Service | Goods | North America
Segment Reporting Information [Line Items]
Gross Profit	2,990	3,207	6,931	4,514
Service | Goods | International
Segment Reporting Information [Line Items]
Gross Profit	4,565	4,506	7,652	8,161
Service | Travel | North America
Segment Reporting Information [Line Items]
Gross Profit	16,303	17,755	32,305	32,920
Service | Travel | International
Segment Reporting Information [Line Items]
Gross Profit	8,919	9,996	19,570	20,032
Product | Goods | North America
Segment Reporting Information [Line Items]
Gross Profit	34,793	33,289	67,774	68,412
Product | Goods | International
Segment Reporting Information [Line Items]
Gross Profit	$ 23,443	$ 17,402	$ 44,695	$ 33,031

SEGMENT INFORMATION Schedule 81

SEGMENT INFORMATION Schedule of Operating Income by Segment (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Operating Income (Loss) by Segment
Total operating income (loss)	[1],[2]	$ (64,245)	$ (7,398)	$ (60,860)	$ (19,078)
Stock-based compensation		16,318	21,440	35,644	41,141
Acquisition related (benefit) expense, net		700		700
Restructuring charges (credits)		(399)	4,584	(116)	7,315
North America
Schedule of Operating Income (Loss) by Segment
Total operating income (loss)	[1],[2]	(68,524)	(12,033)	(70,384)	(26,816)
Stock-based compensation		15,000	20,000	32,900	38,300
Restructuring charges (credits)		177	2,975	177	4,930
International
Schedule of Operating Income (Loss) by Segment
Total operating income (loss)	[1],[2]	4,279	4,635	9,524	7,738
Stock-based compensation		1,300	1,300		2,700
Restructuring charges (credits)		(576)	$ 1,609	(293)	$ 2,385
IBM Lawsuit
Schedule of Operating Income (Loss) by Segment
Provision for loss contingency		$ 75,000		$ 75,000
[1]	(1)Includes stock-based compensation of $15.0 million and $20.0 million for North America and $1.3 million and $1.3 million for International for the three months ended June 30, 2018 and 2017, respectively, and
[2]	Includes restructuring charges (credits) of $0.2 million and $3.0 million for North America and $(0.6) million and $1.6 million for International for the three months ended June 30, 2018 and 2017, respectively

SEGMENT INFORMATION Schedule 82

SEGMENT INFORMATION Schedule of Total Assets by Segment (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	$ 1,488,700	$ 1,677,505
North America
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	871,222	1,045,072
International
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	617,478	632,433
UNITED STATES
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		846,300	1,006,200
IRELAND
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		$ 162,700	$ 219,700
[1]	(1)North America contains assets from the United States of $846.3 million and $1,006.2 million as of June 30, 2018 and December 31, 2017, respectively. International contains assets from Ireland of $162.7 million and $219.7 million as of June 30, 2018 and December 31, 2017, respectively. There were no other individual countries that represented more than 10% of consolidated total assets as of June 30, 2018 and December 31, 2017.