Summary of Available-for-Sale Securities (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 110,282,000	$ 59,478,000
Gross Unrealized Gain	364,000	114,000
Gross Unrealized Loss	(487,000)
Allowance for Credit Loss	0		$ 0
Fair Value	110,159,000	59,592,000
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,733,000	8,860,000
Allowance for Credit Loss	0
Fair Value	10,733,000	8,860,000
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,591,000	15,545,000
Gross Unrealized Gain	274,000	16,000
Allowance for Credit Loss	0
Fair Value	22,865,000	15,561,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	76,958,000	35,073,000
Gross Unrealized Gain	90,000	98,000
Gross Unrealized Loss	(487,000)
Allowance for Credit Loss	0
Fair Value	$ 76,561,000	$ 35,171,000