CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net income (loss)		$ (11,695)	$ 1,988	$ 26,627
Less: Income (loss) from discontinued operations, net of tax		2,597	0	(1,974)
Income (loss) from continuing operations		(14,292)	1,988	28,601
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization of property, equipment and software		91,410	101,330	114,795
Amortization of acquired intangible assets		14,355	14,498	23,032
Stock-based compensation		81,615	64,821	82,044
Gain on sale of intangible assets		0	0	(17,149)
(Gain) loss on sale of investment		412	0	(7,624)
Impairments of investments		9,961	10,156	2,944
Upward adjustment for observable price change of investment		(51,397)	0	0
Deferred income taxes		(1,485)	(5,000)	603
(Gain) loss from changes in fair value of investments		72,497	9,064	(382)
Amortization of debt discount on convertible senior notes		13,200	11,916	10,758
Change in assets and liabilities, net of acquisitions and dispositions:
Accounts receivable		13,577	32,057	(18,793)
Prepaid expenses and other current assets		3,176	7,166	4,074
Right-of-use assets - operating leases		26,226
Accounts payable		(17,401)	5,805	(199)
Accrued merchant and supplier payables		(109,176)	(45,268)	(29,823)
Accrued expenses and other current liabilities		(26,071)	(31,430)	(40,361)
Operating lease obligations		(28,552)
Other, net		(6,772)	13,752	(21,975)
Net cash provided by (used in) operating activities from continuing operations		71,283	190,855	130,545
Net cash provided by (used in) operating activities from discontinued operations		0	0	(2,418)
Net cash provided by (used in) operating activities		71,283	190,855	128,127
Investing activities
Purchases of property and equipment and capitalized software		(67,328)	(69,695)	(59,158)
Proceeds from sale of intangible assets		0	1,500	18,333
Proceeds from sales and maturities of investments		3,475	8,594	16,561
Acquisition of business, net of acquired cash		0	(58,119)	0
Acquisitions of intangible assets and other investing activities		(3,738)	(18,262)	(1,059)
Net cash provided by (used in) investing activities from continuing operations		(67,591)	(135,982)	(25,323)
Net cash provided by (used in) investing activities from discontinued operations		0	0	(9,548)
Net cash provided by (used in) investing activities		(67,591)	(135,982)	(34,871)
Financing activities
Issuance costs for revolving credit agreement		(2,384)	0	0
Payments for repurchases of common stock		(45,631)	(9,585)	(61,233)
Taxes paid related to net share settlements of stock-based compensation awards		(18,105)	(24,105)	(27,681)
Proceeds from stock option exercises and employee stock purchase plan		4,123	5,715	5,513
Distributions to noncontrolling interest holders		(10,935)	(12,576)	(12,357)
Payments of finance lease obligations		(19,687)	(33,023)	(34,025)
Payments of contingent consideration related to acquisitions		0	(1,815)	(7,790)
Payment of financing obligation related to acquisition		0	(8,391)	0
Other financing activities		0	(637)	(473)
Net cash provided by (used in) financing activities		(92,619)	(84,417)	(138,046)
Effect of exchange rate changes on cash, cash equivalents and restricted cash, including cash classified within current assets of discontinued operations		(3,144)	(11,209)	26,499
Net increase (decrease) in cash, cash equivalents and restricted cash, including cash classified within current assets of discontinued operations		(92,071)	(40,753)	(18,291)
Less: Net increase (decrease) in cash classified within current assets of discontinued operations		0	0	(28,866)
Net increase (decrease) in cash, cash equivalents and restricted cash		(92,071)	(40,753)	10,575
Cash, cash equivalents and restricted cash, beginning of period	[1]	844,728	885,481	874,906
Cash, cash equivalents and restricted cash, end of period	[1]	752,657	844,728	885,481
Supplemental disclosure of cash flow information
Income tax payments (refunds)		11,898	2,781	8,646
Cash paid for interest		9,145	9,556	9,425
Non-cash investing and financing activities
Equipment acquired under capital lease arrangements (2)	[2]	0	18,064	28,271
Restricted Cash [Abstract]
Cash, cash equivalents and restricted cash	[1]	752,657	844,728	874,906
Discontinued Operations
Supplemental disclosure of cash flow information
Income tax payments (refunds)		$ 0	$ 0	$ (56)

[1] The following table provides a reconciliation of cash, cash equivalents and restricted cash shown above to amounts reported within the consolidated balance sheets as of December 31, 2019, 2018 and 2017 (in thousands):   December 31, 2019   December 31, 2018   December 31, 2017 Cash and cash equivalents $ 750,887
  $ 841,021
  $ 880,129
Restricted cash included in prepaid expenses and other current assets 1,534
  3,320
  4,932
Restricted cash included in other non-current assets 236
  387
  420
Cash, cash equivalents and restricted cash $ 752,657
  $ 844,728
  $ 885,481

[2] Please refer to Note 10, Leases, for supplemental cash flow information on our leasing obligations, as required by our adoption of Accounting Standards Update ("ASU") 2016-02, Leases ("Topic 842"), on January 1, 2019.