CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net revenue	$ 942,773	$ 850,847	$ 716,063
Costs and expenses:
Cost of revenue (exclusive of depreciation and amortization shown separately below)	57,872	70,518	60,363
Sales and marketing	483,309	437,424	379,895
Product development	212,319	175,787	138,549
General and administrative	120,569	109,707	100,475
Depreciation and amortization	42,807	41,198	35,346
Restructuring and integration	0	288	3,455
Gain on disposal of a business unit	0	(163,697)	0
Total costs and expenses	916,876	671,225	718,083
Income (loss) from operations	25,897	179,622	(2,020)
Other income, net	14,109	4,864	1,694
Income (loss) before income taxes	40,006	184,486	(326)
Benefit from (provision for) income taxes	15,344	(31,491)	(1,385)
Net income (loss) attributable to common stockholders	$ 55,350	$ 152,995	$ (1,711)
Net income (loss) per share attributable to common stockholders
Basic (in dollars per share)	$ 0.66	$ 1.87	$ (0.02)
Diluted (in dollars per share)	$ 0.62	$ 1.76	$ (0.02)
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders
Basic (in shares)	83,573	81,602	77,186
Diluted (in shares)	88,709	87,170	77,186