Significant Accounting Policies - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended				12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Aug. 31, 2018 USD ($) $ / shares shares	Nov. 30, 2017 $ / shares shares	May 31, 2017 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) agency segment	Dec. 31, 2018 USD ($) agency	Dec. 31, 2017 USD ($) agency	Feb. 28, 2019 USD ($)	Jan. 01, 2019 USD ($)	Oct. 31, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Proceeds from initial public offering, net of underwriting discounts					$ 0	$ 0	$ 80,213
Deferred offering costs				$ 2,400
Contract assets balances					22,800				$ 25,800
Contract liabilities revenue recognized					66,600
Unsatisfied performance obligations					175,800
Tenant improvement allowance receivable					0	14,400				$ 15,800
Additional tenant improvement allowance receivable								$ 2,600
Tenant improvement allowance received					$ 17,000
Capitalized contract cost, amortization period					5 years
Commission expense					$ 15,684	15,600	11,800
Number of operating segments | segment					1
Number of reportable segments | segment					1
Foreign currency transaction gains (losses)					$ (200)	(3,000)	2,600
Advertising expense					4,100	3,900	$ 3,000
Adjustment to accumulated deficit					(135,413)	$ (145,640)
Adoption of ASC 606					5,094
Accounting Standards Update 2014-09
Summary Of Significant Accounting Policies [Line Items]
Adjustment to accumulated deficit									(55,800)
Decrease in total deferred revenue									(35,400)
Addition of contract asset									20,400
Adoption of ASC 606					$ 5,100
Total lease liability recognized upon adoption									51,400
ROU assets recognized upon adoption									$ 33,800
Customer Concentration Risk | Sales Revenue, Net | Foreign Customers
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage					32.30%	28.70%	27.00%
Customer Concentration Risk | Sales Revenue, Net | Government Agencies
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage					17.10%	15.70%	15.40%
Customer Concentration Risk | Sales Revenue, Net | Federal Government Agencies
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage					7.40%	7.80%	8.40%
Number of federal government agencies | agency					3	3	3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Summary Of Significant Accounting Policies [Line Items]
Unsatisfied performance obligations					$ 153,700
Revenue, remaining performance obligation, period					24 months
Minimum
Summary Of Significant Accounting Policies [Line Items]
SaaS Subscriptions contracts term					1 year
Term license subscription contracts term					1 year
Maximum
Summary Of Significant Accounting Policies [Line Items]
SaaS Subscriptions contracts term					3 years
Term license subscription contracts term					3 years
Class A Common Stock
Summary Of Significant Accounting Policies [Line Items]
Number of shares issued in public offering (in shares) | shares		2,000,000
Sale of stock, offering price (in usd per share) | $ / shares		$ 35.15
Proceeds from initial public offering, net of underwriting discounts				$ 77,800
Number of shares issued by the company in public offering (in shares) | shares		1,675,000
Number of shares issued by sharesholders in public offering (in shares) | shares		325,000
Net proceeds from public offering		$ 57,800
Initial Public Offering | Class A Common Stock
Summary Of Significant Accounting Policies [Line Items]
Number of shares issued in public offering (in shares) | shares				7,187,500
Sale of stock, offering price (in usd per share) | $ / shares				$ 12.00
Secondary Offering | Class A Common Stock
Summary Of Significant Accounting Policies [Line Items]
Number of shares issued in public offering (in shares) | shares			4,370,000
Sale of stock, offering price (in usd per share) | $ / shares			$ 20.25
Public Offering | Class A Common Stock
Summary Of Significant Accounting Policies [Line Items]
Number of shares issued in public offering (in shares) | shares	2,329,000
Sale of stock, offering price (in usd per share) | $ / shares	$ 55.70
Number of shares issued by the company in public offering (in shares) | shares	1,825,000
Number of shares issued by sharesholders in public offering (in shares) | shares	504,000
Net proceeds from public offering	$ 101,300
Computer software
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life					3 years
Computer hardware
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life					3 years
Equipment
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life					5 years
Office furniture and fixtures
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life					10 years