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Summary of Available-for-Sale Securities (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 87,376,000	$ 102,529,000
Gross Unrealized Gain	461,000	677,000
Gross Unrealized Loss	(5,000)	(3,000)
Allowance for Credit Loss	0	0	$ 0
Fair Value	87,832,000	103,203,000
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,714,000	6,203,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Allowance for Credit Loss	0	0
Fair Value	13,714,000	6,203,000
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,050,000	29,570,000
Gross Unrealized Gain	32,000	66,000
Gross Unrealized Loss	0	0
Allowance for Credit Loss	0	0
Fair Value	20,082,000	29,636,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53,612,000	66,756,000
Gross Unrealized Gain	429,000	611,000
Gross Unrealized Loss	(5,000)	(3,000)
Allowance for Credit Loss	0	0
Fair Value	$ 54,036,000	$ 67,364,000

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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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