Summary of Available-for-Sale Securities (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 102,529,000	$ 59,478,000
Gross Unrealized Gain	677,000	114,000
Gross Unrealized Loss	(3,000)	0
Allowance for Credit Loss	0	0	$ 0
Fair Value	103,203,000	59,592,000
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,203,000	8,860,000
Gross Unrealized Loss	0	0
Allowance for Credit Loss	0	0
Fair Value	6,203,000	8,860,000
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,570,000	15,545,000
Gross Unrealized Gain	66,000	16,000
Gross Unrealized Loss	0	0
Allowance for Credit Loss	0	0
Fair Value	29,636,000	15,561,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66,756,000	35,073,000
Gross Unrealized Gain	611,000	98,000
Gross Unrealized Loss	(3,000)	0
Allowance for Credit Loss	0	0
Fair Value	$ 67,364,000	$ 35,171,000