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Summary of Available-for-Sale Securities (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 112,627,000	$ 59,478,000
Gross Unrealized Gain	909,000	114,000
Gross Unrealized Loss	(2,000)
Allowance for Credit Loss	0		$ 0
Fair Value	113,534,000	59,592,000
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,360,000	8,860,000
Allowance for Credit Loss	0
Fair Value	7,360,000	8,860,000
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	33,602,000	15,545,000
Gross Unrealized Gain	127,000	16,000
Gross Unrealized Loss	(2,000)
Allowance for Credit Loss	0
Fair Value	33,727,000	15,561,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	71,665,000	35,073,000
Gross Unrealized Gain	782,000	98,000
Allowance for Credit Loss	0
Fair Value	$ 72,447,000	$ 35,171,000

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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