Contract Assets and Liabilites - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	53,500,000	45,900,000	$ 111,600,000	103,900,000
Revenue expected to be recognized	325,000,000		325,000,000
Amortization expense related to deferred commissions	$ 8,900,000	$ 8,200,000	$ 16,000,000	$ 15,200,000
Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with customer, expected payment term			one year