CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]	Sep. 30, 2018	Sep. 30, 2017	[1]
Income Statement [Abstract]
Net revenue	$ 241,096	$ 223,287		$ 699,033	$ 631,406
Costs and expenses:
Cost of revenue (exclusive of depreciation and amortization shown separately below)	14,177	19,312		43,618	54,282
Sales and marketing	121,759	112,958		362,054	326,409
Product development	53,764	45,834		158,046	127,793
General and administrative	30,302	27,601		90,892	81,808
Depreciation and amortization	10,713	10,656		31,250	31,470	[2]
Restructuring and integration	0	35		0	286
Total costs and expenses	230,715	216,396		685,860	622,048
Income from operations	10,381	6,891		13,173	9,358
Other income, net	3,921	1,371		9,950	2,933
Income before income taxes	14,302	8,262		23,123	12,291
Benefit from (provision for) income taxes	684	(232)		281	(417)
Net income attributable to common stockholders	$ 14,986	$ 8,030		$ 23,404	$ 11,874	[2]
Net income per share attributable to common stockholders
Basic (in USD per share)	$ 0.18	$ 0.10		$ 0.28	$ 0.15
Diluted (in USD per share)	$ 0.17	$ 0.09		$ 0.26	$ 0.14
Weighted-average shares used to compute net income per share attributable to common stockholders
Basic (in shares)	84,008	82,259		83,865	81,041
Diluted (in shares)	88,724	87,433		89,271	86,097

[1] As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior periods presented. See Note 1 below for additional discussion.

[2] As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.