Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Software development cost, net of impairment	$ 8.3	$ 2.5
Internal-use software development costs	11.9	4.4
Advertising Expense	$ 42.4	41.6	$ 34.3
Number of reportable segment | Segment	1
Accounting Standards Update 2014-09
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Deffered contract costs, expected amortization period of benefit	5 years
Deferred costs of sales commission	$ 53.3	$ 33.4
Minimum
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Contractual arrangement subscriptions period	1 month
Maximum
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Contractual arrangement subscriptions period	3 years
Accounts receivable | Customer concentration risk
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage	18.00%	30.00%
Revenues | Customer concentration risk
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage	11.00%	14.00%	13.00%
Software subscription revenues | Customer concentration risk
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage	12.00%	13.00%	12.00%