Contract Assets and Liabilities - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract assets	$ 0	$ 0	$ 0	$ 0
Contract with customer, contract duration			1 year
Deferred revenue recognized	21,200,000	24,700,000	$ 132,800,000	128,600,000
Revenue expected to be recognized	307,600,000		307,600,000
Amortization expense related to deferred commissions	$ 8,100,000	$ 7,200,000	$ 24,100,000	$ 22,400,000
Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with customer, expected payment term			one year