Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net income	$ 95,894	$ 77,491	$ 81,800
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	44,395	38,231	26,559
Depreciation and amortization expense	48,031	26,742	27,197
Bad debt expense	10,963	4,124	2,497
Foreign exchange (gain) loss	(5,708)	5,997	(27,424)
Amortization of debt issuance costs	2,006	1,191	463
Non-cash interest expense	19,108	10,968	3,117
Interest (income) expense on marketable securities	(4,182)	(2,887)	426
Loss on disposal of assets	1,667	136	520
Asset impairment charges	0	0	3,162
Deferred income taxes	(15,248)	(22,414)	(49,535)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(12,656)	17,215	(8,826)
Funds receivable and seller accounts	(23,177)	23,436	(13,477)
Prepaid expenses and other current assets	(14,156)	(4,785)	3,024
Other assets	4,045	43	(28)
Accounts payable	(953)	13,364	2,837
Accrued and other current liabilities	37,410	23,079	(2,659)
Funds payable and amounts due to sellers	23,177	(23,436)	13,477
Deferred revenue	191	1,331	434
Other liabilities	(3,887)	9,099	5,537
Net cash provided by operating activities	206,920	198,925	69,101
Cash flows from investing activities
Cash paid for asset acquisition and intangible assets	(1,963)	(35,494)	0
Acquisition of businesses, net of cash acquired	(270,409)	0	0
Purchases of property and equipment	(7,528)	(1,019)	(3,948)
Development of internal-use software	(7,750)	(19,537)	(9,208)
Purchases of marketable securities	(661,821)	(514,286)	(62,348)
Sales of marketable securities	461,098	284,943	137,340
Net cash (used in) provided by investing activities	(488,373)	(285,393)	61,836
Cash flows from financing activities
Payment of tax obligations on vested equity awards	(32,547)	(24,065)	(6,417)
Repurchase of stock	(176,985)	(134,647)	(10,301)
Proceeds from exercise of stock options	9,791	18,253	33,838
Proceeds from issuance of convertible senior notes	650,000	345,000	0
Payment of debt issuance costs	(11,904)	(9,962)	0
Purchase of capped call	(76,180)	(34,224)	0
Payments on finance lease obligations	(10,833)
Payments on finance lease obligations		(6,057)	(7,798)
Payments on facility financing obligation	0	(10,164)	(5,883)
Other financing, net	8,265	(128)	3,116
Net cash provided by financing activities	359,607	144,006	6,555
Effect of exchange rate changes on cash	(1,846)	(5,995)	(3,642)
Net increase in cash, cash equivalents, and restricted cash	76,308	51,543	133,850
Cash, cash equivalents, and restricted cash at beginning of period	372,326	320,783	186,933
Cash, cash equivalents, and restricted cash at end of period	448,634	372,326	320,783
Supplemental cash flow disclosures:
Cash paid for interest	3,206	10,002	7,555
Cash paid for income taxes	2,084	966	1,003
Supplemental non-cash disclosures:
Stock-based compensation capitalized in development of capitalized software	1,302	2,252	807
Additions to development of internal-use software and property and equipment included in accounts payable and accrued expenses	1,148	1,211	956
Right-of-assets obtained in exchange for new lease liabilities:
Finance Leases	849
Finance Leases		2,122	5,586
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Total cash, cash equivalents, and restricted cash	$ 372,326	$ 372,326	$ 186,933