Summary of Available-for-Sale Securities (Detail) - USD ($)	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 87,682,000	$ 102,529,000
Gross Unrealized Gain	319,000	677,000
Gross Unrealized Loss	(2,000)	(3,000)
Allowance for Credit Loss	0	0	$ 0
Fair Value	87,999,000	103,203,000
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,188,000	6,203,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Allowance for Credit Loss	0	0
Fair Value	24,188,000	6,203,000
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,037,000	29,570,000
Gross Unrealized Gain	11,000	66,000
Gross Unrealized Loss	(1,000)	0
Allowance for Credit Loss	0	0
Fair Value	16,047,000	29,636,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47,457,000	66,756,000
Gross Unrealized Gain	308,000	611,000
Gross Unrealized Loss	(1,000)	(3,000)
Allowance for Credit Loss	0	0
Fair Value	$ 47,764,000	$ 67,364,000