CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue
Total revenue	$ 64,435	$ 60,873	$ 59,130	$ 59,906	$ 54,506	$ 52,068	$ 49,391	$ 51,904	$ 244,344	$ 207,869	$ 178,646
Cost of revenue
Total cost of revenue	17,394	15,659	16,296	16,511	16,089	15,652	14,286	14,218	65,860	60,245	51,625
Gross profit	47,041	45,214	42,834	43,395	38,417	36,416	35,105	37,686	178,484	147,624	127,021
Operating expenses
Research and development	20,773	19,984	20,718	20,127	18,870	17,527	16,239	15,536	81,602	68,172	57,438
Sales and marketing	23,011	24,068	22,252	21,006	21,949	23,712	19,787	18,713	90,337	84,161	80,466
General and administrative	11,047	11,864	21,654	11,768	12,271	8,959	8,943	9,421	56,333	39,594	32,695
Total operating expenses	54,831	55,916	64,624	52,901	53,090	50,198	44,969	43,670	228,272	191,927	170,599
Loss from operations	(7,790)	(10,702)	(21,790)	(9,506)	(14,673)	(13,782)	(9,864)	(5,984)	(49,788)	(44,303)	(43,578)
Interest expense	(480)	(448)	(449)	(450)	(451)	(464)	(475)	(455)	(1,827)	(1,845)	(1,875)
Other income, net	753	203	492	343	797	198	176	612	1,791	1,783	1,500
Loss before provision for income taxes	(7,517)	(10,947)	(21,747)	(9,613)	(14,327)	(14,048)	(10,163)	(5,827)	(49,824)	(44,365)	(43,953)
Provision for income taxes	204	17	21	5	(6)	25	33	9	247	61	24
Net loss	$ (7,721)	$ (10,964)	$ (21,768)	$ (9,618)	$ (14,321)	$ (14,073)	$ (10,196)	$ (5,836)	$ (50,071)	$ (44,426)	$ (43,977)
Net loss per common share:
Basic and diluted (in dollars per share)	$ (0.17)	$ (0.25)	$ (0.50)	$ (0.22)	$ (0.34)	$ (0.34)	$ (0.25)	$ (0.14)	$ (1.15)	$ (1.07)	$ (1.08)
Weighted-average common shares outstanding - basic and diluted (in shares)	44,472,672	43,973,428	43,234,655	42,858,756	42,108,764	41,815,139	41,429,691	41,108,611	43,640,408	41,618,838	40,671,133
Subscription and support
Revenue
Total revenue	$ 53,779	$ 51,306	$ 48,837	$ 46,470	$ 45,549	$ 43,214	$ 40,980	$ 39,540	$ 200,392	$ 169,283	$ 143,120
Cost of revenue
Total cost of revenue	8,637	8,139	8,637	8,802	8,779	8,472	7,758	7,637	34,215	32,646	27,895
Professional services
Revenue
Total revenue	10,656	9,567	10,293	13,436	8,957	8,854	8,411	12,364	43,952	38,586	35,526
Cost of revenue
Total cost of revenue	$ 8,757	$ 7,520	$ 7,659	$ 7,709	$ 7,310	$ 7,180	$ 6,528	$ 6,581	$ 31,645	$ 27,599	$ 23,730