Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Payment terms			The Company’s standard payment terms are generally within 180 days of invoicing. If extended payment terms are granted to customers, those terms generally do not exceed one year.
Description of warranty			The standard software assurance warranty period is generally less than one year.
Amortization period for capitalized contract costs	3 years		3 years
Product support period			1 year
Capitalized cost to obtain customer contracts net	$ 3.9		$ 3.9		$ 4.5
Sales and Marketing
Summary Of Significant Accounting Policies [Line Items]
Amortization expenses related to capitalized cost	$ 0.6	$ 0.8	$ 1.6	$ 2.2