CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net revenue		$ 222,380	$ 186,232	$ 628,567	$ 518,273
Costs and expenses:
Cost of revenue (exclusive of depreciation and amortization shown separately below)		19,312	14,594	54,282	44,759
Sales and marketing		113,041	99,274	327,559	289,304
Product development		45,834	36,369	127,793	101,689
General and administrative		26,694	24,876	78,969	70,109
Depreciation and amortization		10,656	9,159	31,470	25,912
Restructuring and integration		35	0	286	0
Total costs and expenses		215,572	184,272	620,359	531,773
Income (loss) from operations		6,808	1,960	8,208	(13,500)
Other income, net		1,371	327	2,933	952
Income (loss) before income taxes		8,179	2,287	11,141	(12,548)
Provision for income taxes		(232)	(217)	(417)	(385)
Net income (loss) attributable to common stockholders	[1]	$ 7,947	$ 2,070	$ 10,724	$ (12,933)
Net income (loss) per share attributable to common stockholders
Basic (in USD per share)	[1]	$ 0.10	$ 0.03	$ 0.13	$ (0.17)
Diluted (in USD per share)	[1]	$ 0.09	$ 0.02	$ 0.12	$ (0.17)
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders
Basic (in shares)	[1]	82,259	77,521	81,041	76,627
Diluted (in shares)	[1]	87,433	82,917	86,097	76,627

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