CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue	$ 61,660	$ 54,074	$ 119,901	$ 104,993
Costs and expenses
Cost of revenue	16,036	15,134	29,990	28,915
Sales and marketing	25,392	23,392	49,523	45,092
General and administrative	11,499	10,437	21,622	20,130
Product development	14,219	9,326	27,471	19,285
Restructuring costs	1,906	2,076	2,084	2,315
Amortization of purchased intangibles	424	470	848	942
Total costs and expenses	69,476	60,835	131,538	116,679
Loss from operations	(7,816)	(6,761)	(11,637)	(11,686)
Other income (expense), net	31	(99)	160	221
Loss before provision for income taxes	(7,785)	(6,860)	(11,477)	(11,465)
Provision for income taxes	536	673	47	1,744
Net loss	$ (8,321)	$ (7,533)	$ (11,524)	$ (13,209)
Net loss per share of common stock:
Basic net loss per common share (in dollars per share)	$ (0.14)	$ (0.13)	$ (0.20)	$ (0.24)
Diluted net loss per common share (in dollars per share)	$ (0.14)	$ (0.13)	$ (0.20)	$ (0.24)
Weighted-average shares used to compute net loss per share:
Weighted average shares outstanding used in basic net loss per common share calculation (in shares)	58,648,195	55,954,158	57,982,648	55,964,568
Weighted average shares outstanding used in diluted net loss per common share calculation (in shares)	58,648,195	55,954,158	57,982,648	55,964,568
Cost of revenue
Costs and expenses
Amortization of purchased intangibles			$ 574	$ 1,918
Additional Information on Operating Expenses
Stock-based compensation expense	$ 230	$ 117	384	193
Depreciation expense	1,931	1,870	3,847	3,635
Amortization of purchased intangibles	287	959
Sales and marketing
Additional Information on Operating Expenses
Stock-based compensation expense	1,373	754	2,259	1,408
Depreciation expense	371	408	727	789
General and administrative
Additional Information on Operating Expenses
Stock-based compensation expense	1,182	774	2,022	1,436
Depreciation expense	274	340	520	590
Product development
Additional Information on Operating Expenses
Stock-based compensation expense	1,041	702	1,599	1,223
Depreciation expense	$ 852	$ 427	$ 1,692	$ 824