Schedule of Amortization of Deferred Contract Costs (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Deferred Financing Cost [Line Items]
Amortization of deferred contract costs	[1]	$ 3,809	$ 2,902	$ 7,598	$ 5,496

[1] Included in selling and marketing expenses in the unaudited condensed consolidated statement of operations.