CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES:
Net income (loss)	[1]	$ 10,724	$ (12,933)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization		31,470	25,912
Provision for doubtful accounts and sales returns		13,448	12,139
Stock-based compensation		75,007	62,396
Other adjustments		411	1,314
Changes in operating assets and liabilities:
Accounts receivable		(16,971)	(24,167)
Prepaid expenses and other assets		(2,106)	3,638
Accounts payable, accrued expenses and other liabilities		15,628	13,193
Deferred revenue		350	295
Net cash provided by operating activities		127,961	81,787
INVESTING ACTIVITIES:
Purchases of marketable securities		(179,557)	(221,771)
Maturities of marketable securities		191,000	212,500
Purchase of cost-method investment		0	(8,000)
Acquisitions of businesses, net of cash received		(50,544)	0
Purchases of property, equipment and software		(7,892)	(17,798)
Capitalized website and software development costs		(12,236)	(10,596)
Other investing activities		(1,209)	(927)
Net cash used in investing activities		(60,438)	(46,592)
FINANCING ACTIVITIES:
Proceeds from issuance of common stock for employee stock-based plans		29,556	18,055
Cash used for common stock repurchases		(7,743)	0
Net cash provided by financing activities		21,813	18,055
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS		864	28
CHANGE IN CASH AND CASH EQUIVALENTS		90,200	53,278
CASH AND CASH EQUIVALENTS—Beginning of period		272,201	171,613
CASH AND CASH EQUIVALENTS—End of period		362,401	224,891
SUPPLEMENTAL DISCLOSURES OF OTHER CASH FLOW INFORMATION:
Cash paid for income taxes, net		82	688
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property, equipment and software recorded in accounts payable, accrued expenses and other liabilities		3,555	4,373
Goodwill measurement period adjustment		$ (178)	$ 146

[1] The structure of the Company’s common stock changed during the year ended December 31, 2016. Refer to Note 13 for details.