Summary of Available-for-Sale Securities (Detail) - USD ($)	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 116,233,000	$ 59,478,000
Gross Unrealized Gain	1,128,000	114,000
Gross Unrealized Loss	(3,000)
Allowance for Credit Loss	0		$ 0
Fair Value	117,358,000	59,592,000
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,788,000	8,860,000
Allowance for Credit Loss	0
Fair Value	15,788,000	8,860,000
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,564,000	15,545,000
Gross Unrealized Gain	182,000	16,000
Allowance for Credit Loss	0
Fair Value	18,746,000	15,561,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	81,881,000	35,073,000
Gross Unrealized Gain	946,000	98,000
Gross Unrealized Loss	(3,000)
Allowance for Credit Loss	0
Fair Value	$ 82,824,000	$ 35,171,000