Summary of Significant Accounting Policies - Statement of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 244,091	$ 200,940	$ 157,437
Cost of revenue:
Total cost of revenue	71,083	56,910	39,725
Total gross profit	173,008	144,030	117,712
Operating expenses:
Research and development	67,743	50,938	47,955
Sales and marketing	123,310	111,593	90,524
General and administrative	34,993	30,293	28,282
Total operating expenses	226,046	192,824	166,761
Loss from operations	(53,038)	(48,794)	(49,049)
Other income (expense), net:
Interest income	3,229	862	342
Interest expense	(4,934)	(87)	(211)
Other income (expense), net	(336)	313	(109)
Loss before income taxes	(55,079)	(47,706)	(49,027)
Provision for (benefit from) income taxes	466	(2,236)	(27)
Net loss	$ (55,545)	$ (45,470)	$ (49,000)
Net loss per share, basic and diluted (in dollars per share)	$ (1.20)	$ (1.06)	$ (1.19)
Weighted-average common shares outstanding, basic and diluted (in shares)	46,456,825	42,952,950	41,248,473
Product [Member]
Revenue:
Total revenue	$ 168,571	$ 116,748	$ 89,404
Cost of revenue:
Total cost of revenue	39,810	25,583	12,447
Maintenance [Member]
Revenue:
Total revenue	42,223	46,268	37,403
Cost of revenue:
Total cost of revenue	7,678	7,491	7,105
Professional Services [Member]
Revenue:
Total revenue	33,297	37,924	30,630
Cost of revenue:
Total cost of revenue	23,595	$ 23,836	$ 20,173
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue:
Total revenue	255,923
Cost of revenue:
Total cost of revenue	71,016
Total gross profit	184,907
Operating expenses:
Research and development	67,743
Sales and marketing	136,167
General and administrative	34,993
Total operating expenses	238,903
Loss from operations	(53,996)
Other income (expense), net:
Interest income	3,229
Interest expense	(4,934)
Other income (expense), net	(336)
Loss before income taxes	(56,037)
Provision for (benefit from) income taxes	157
Net loss	$ (56,194)
Net loss per share, basic and diluted (in dollars per share)	$ (1.21)
Weighted-average common shares outstanding, basic and diluted (in shares)	46,456,825
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Product [Member]
Revenue:
Total revenue	$ 175,146
Cost of revenue:
Total cost of revenue	39,761
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Maintenance [Member]
Revenue:
Total revenue	45,767
Cost of revenue:
Total cost of revenue	7,678
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Professional Services [Member]
Revenue:
Total revenue	35,010
Cost of revenue:
Total cost of revenue	$ 23,577