Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018	Dec. 31, 2014
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Cash equivalents	$ 51,562	$ 53,148	$ 86,553		$ 36,823
Restricted cash	200
Unamortized capitalized costs relating to software acquired for internal use	1,100	0
Cumulative-effect adjustment for the adoption of ASU 2016-09	$ 0
Revenue recognition period	5 years
Expected [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Contract with Customer, Asset, Net				$ 28,000
Nonoperating Income (Expense) [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Foreign currency transactional (gain) losses	$ (100)		100
Foreign currency re-measurement (gain) losses	(400)	100	200
Sales and Marketing [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Advertising costs	8,400	6,000	$ 4,300
Money Market Funds [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Cash equivalents	$ 100	11,000
Accounting Standards Update 2016-09 [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Increase to deferred tax assets		3,400
Accounting Standards Update 2016-09 [Member] | Accumulated Deficit [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Cumulative-effect adjustment for the adoption of ASU 2016-09		$ (100)
Minimum [Member] | Maintenance and Support [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Contractual period	1 year
Minimum [Member] | All other asset categories [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Useful life	3 years
Maximum [Member] | Maintenance and Support [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Contractual period	3 years
Maximum [Member] | All other asset categories [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure And Significant Accounting Policies [Line Items]
Useful life	5 years