Stockholders' Equity - Stock-Based Compensation Expense Related to Grants of Employee and Consultant Stock Options, Restricted Stock and Restricted Stock Units (ZSUs) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 15,589	$ 24,475	$ 49,346	$ 80,982
Cost of Revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	435	1,049	1,425	2,825
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	10,097	18,662	32,293	63,078
Sales and Marketing [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,891	1,541	5,429	5,738
General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 3,166	$ 3,223	$ 10,199	$ 9,341