Equity Incentive Plans - Recorded Stock-Based Compensation Expense in the Condensed Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Payment Arrangement, Expensed [Line Items]
Stock-based compensation expense	$ 13,333	$ 2,658	$ 1,661
Cost of revenue [Member]
Share-based Payment Arrangement, Expensed [Line Items]
Stock-based compensation expense	325	85	44
Research and development [Member]
Share-based Payment Arrangement, Expensed [Line Items]
Stock-based compensation expense	5,721	1,030	801
Selling, general and administrative [Member]
Share-based Payment Arrangement, Expensed [Line Items]
Stock-based compensation expense	$ 7,287	$ 1,543	$ 816