Organization, Basis of Presentation and Summary of Significant Accounting Policies - Condensed Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Organization And Summary Of Significant Accounting Policies [Line Items]
Net loss	$ (49,670)	$ (41,477)
Changes in deferred revenue	118,540	$ 56,078
Adjustments [Member] | Topic 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Net loss	(8,495)
Changes in deferred revenue	8,495
Balances without adoption of Topic 606 [Member] | Topic 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Net loss	(58,165)
Changes in deferred revenue	$ 127,035