Segment Information (Summary of Financial Information by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue:
Revenue	$ 64,213	$ 56,493	$ 184,114	$ 161,486
Cost of revenue	15,689	14,541	45,679	43,456
Sales and marketing	26,748	21,603	76,271	66,695
Amortization of purchased intangibles	424	470	1,272	1,412
Unallocated corporate expenses	26,178	20,124	77,355	61,854
Loss from operations	(4,826)	(245)	(16,463)	(11,931)
Corporate
Revenue:
Unallocated corporate expenses	26,178	20,124	77,355	61,854
Loss from operations	(26,178)	(20,124)	(77,355)	(61,854)
Business | Operating Segments
Revenue:
Revenue	59,337	52,138	169,606	148,501
Cost of revenue	14,695	13,681	42,699	40,794
Sales and marketing	24,391	19,554	69,453	60,338
Amortization of purchased intangibles	424	470	1,272	1,412
Loss from operations	19,827	18,433	56,182	45,957
Consumer | Operating Segments
Revenue:
Revenue	4,876	4,355	14,508	12,985
Cost of revenue	994	860	2,980	2,662
Sales and marketing	2,357	2,049	6,818	6,357
Loss from operations	1,525	1,446	4,710	3,966
Hosted Services - Business
Revenue:
Revenue	50,046	46,378	145,805	131,798
Hosted Services - Business | Business | Operating Segments
Revenue:
Revenue	50,046	46,378	145,805	131,798
Hosted Services - Consumer
Revenue:
Revenue	4,876	4,355	14,508	12,985
Hosted Services - Consumer | Consumer | Operating Segments
Revenue:
Revenue	4,876	4,355	14,508	12,985
Professional Services
Revenue:
Revenue	9,291	5,760	23,801	16,703
Professional Services | Business | Operating Segments
Revenue:
Revenue	$ 9,291	$ 5,760	$ 23,801	$ 16,703