Stockholders' Equity - Stock-Based Compensation Expense Related to Grants of Employee Stock Options, Restricted Stock Units (RSUs) and Performance and Market Based Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 38,724	$ 21,339	$ 84,862	$ 61,467
Cost of Revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	566	407	1,548	1,088
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	25,380	12,029	48,595	35,982
Sales and Marketing [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	3,957	3,046	10,960	8,453
General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 8,821	$ 5,857	$ 23,759	$ 15,944