Cash, Cash Equivalents and Investments - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents maturities	90 days	90 days
Investment of cash equivalents are redeemable upon demand using amortized cost method	$ 1.00
Investment in money market funds restricted by investment in short term securities, percentage	100.00%
Short-term investments, maturities, minimum	90 days
Short-term investments, maturities, maximum	1 year
Long-term investments, maturities, minimum	1 year
Long-term investments, maturities, maximum	2 years
Net unrealized gains (losses)	$ 0	$ (10,000)
China [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents in foreign bank	1,100,000	$ 2,100,000
Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Federal Deposit Insurance Corporation insured limit	$ 250,000