Description of Business and Basis of Presentation - Summary of Unaudited Consolidated Statement of Operations Reflecting Adoption of Topic 606 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue	$ 55,239	$ 43,203	$ 153,293	$ 116,220
Cost of revenues	16,138	12,523	44,721	33,258
Gross profit	39,101	30,680	108,572	82,962
Operating expenses:
Sales and marketing	25,641	21,397	73,670	58,596
Loss before income taxes	(11,397)	(11,339)	(35,571)	(32,957)
Income tax expense	(75)	(132)	(307)	(383)
Net loss	$ (11,472)	$ (11,471)	$ (35,878)	$ (33,340)
Net loss per common share, basic and diluted	$ (0.33)	$ (0.39)	$ (1.06)	$ (1.14)
Subscription and Support
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue	$ 49,235	$ 38,290	$ 137,539	$ 103,557
Cost of revenues	12,149	9,278	33,324	24,350
Professional Services and Other
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue	6,004	4,913	15,754	12,663
Cost of revenues	$ 3,989	3,245	$ 11,397	8,908
As Previously Reported | Adoption of New Standard
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue		42,948		114,971
Gross profit		30,478		81,892
Operating expenses:
Sales and marketing		22,129		62,429
Loss before income taxes		(12,302)		(37,893)
Income tax expense		(71)		(207)
Net loss		$ (12,373)		$ (38,100)
Net loss per common share, basic and diluted		$ (0.42)		$ (1.31)
As Previously Reported | Subscription and Support | Adoption of New Standard
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue		$ 37,427		$ 100,590
As Previously Reported | Professional Services and Other | Adoption of New Standard
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue		5,521		14,381
Cost of revenues		3,192		8,729
Adjustments | Adoption of New Standard
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue		255		1,249
Gross profit		202		1,070
Operating expenses:
Sales and marketing		(732)		(3,833)
Loss before income taxes		963		4,936
Income tax expense		(61)		(176)
Net loss		$ 902		$ 4,760
Net loss per common share, basic and diluted		$ 0.03		$ 0.17
Adjustments | Subscription and Support | Adoption of New Standard
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue		$ 863		$ 2,967
Adjustments | Professional Services and Other | Adoption of New Standard
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue		(608)		(1,718)
Cost of revenues		$ 53		$ 179