Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 48,486,000	$ 37,642,000	$ 37,870,000	$ 32,416,000	$ 41,432,000	$ 29,729,000	$ 28,648,000	$ 24,876,000	$ 156,414,000	$ 124,685,000
Cost of revenue	13,321,000	13,869,000	15,085,000	15,116,000	15,489,000	14,687,000	15,044,000	14,783,000	57,391,000	60,003,000
Sales and marketing	11,414,000	11,040,000	11,519,000	10,592,000	10,510,000	10,654,000	11,135,000	12,257,000	44,565,000	44,556,000
Technology and development	10,421,000	10,293,000	9,839,000	9,716,000	8,825,000	9,299,000	9,245,000	10,494,000	40,269,000	37,863,000
General and administrative	12,344,000	9,121,000	10,027,000	10,280,000	9,091,000	9,355,000	11,441,000	12,544,000	41,772,000	42,431,000
Restructuring and other exit costs	0	0	0	0	0	0	974,000	2,466,000	0	3,440,000
Total expenses	47,500,000	44,323,000	46,470,000	45,704,000	43,915,000	43,995,000	47,839,000	52,544,000	183,997,000	188,293,000
Loss from operations	986,000	(6,681,000)	(8,600,000)	(13,288,000)	(2,483,000)	(14,266,000)	(19,191,000)	(27,668,000)	(27,583,000)	(63,608,000)
Total other (income) expense, net	(406,000)	562,000	403,000	34,000	377,000	558,000	1,281,000	(73,000)	593,000	2,143,000
Loss before income taxes	580,000	(6,119,000)	(8,197,000)	(13,254,000)	(2,106,000)	(13,708,000)	(17,910,000)	(27,741,000)	(26,990,000)	(61,465,000)
Provision (benefit) for income taxes	(943,000)	55,000	84,000	(708,000)	124,000	84,000	74,000	75,000	(1,512,000)	357,000
Net loss	$ 1,523,000	$ (6,174,000)	$ (8,281,000)	$ (12,546,000)	$ (2,230,000)	$ (13,792,000)	$ (17,984,000)	$ (27,816,000)	$ (25,478,000)	$ (61,822,000)
Basic (usd per share)	$ 0.03	$ (0.12)	$ (0.16)	$ (0.24)	$ (0.04)	$ (0.27)	$ (0.36)	$ (0.56)
Diluted (usd per share)		$ (0.12)	$ (0.16)	$ (0.24)	$ (0.04)	$ (0.27)	$ (0.36)	$ (0.56)	$ 0.03
Basic (in shares)	53,473	53,023	52,358	51,577	50,746	50,513	50,071	49,692
Diluted (in shares)		53,023	52,358	51,577	50,746	50,513	50,071	49,692	59,595