Investments in Marketable Securities - Summary of Investments Classified As Available-For-Sale Securities (Parenthetical) (Detail)	Mar. 31, 2021 USD ($) Security	Dec. 31, 2020 USD ($) Security
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized gain position \| Security	26	38
Unrealized gains, aggregate	$ 46,000	$ 94,000
Number of securities in unrealized loss position \| Security	83	80
Unrealized losses, aggregate	$ 150,000	$ 148,000
Short-term investments - available for sale	224,874,000	219,269,000
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments - available for sale	42,962,000	27,973,000
Short-term investments classified as available-for-sale, noncurrent	52,900,000	53,400,000
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains, aggregate	46,000	94,000
Unrealized losses, aggregate	136,000	136,000
Short-term investments - available for sale	172,665,000	185,669,000
Short-term investments classified as available-for-sale, noncurrent	52,900,000	53,400,000
Government debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses, aggregate	14,000	12,000
Short-term investments - available for sale	9,247,000	5,627,000
Short-term investments classified as available-for-sale, noncurrent	52,900,000	53,400,000
Cash equivalents [Member] \| Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments - available for sale	0	0
Cash equivalents [Member] \| Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments - available for sale	0	0
Cash equivalents [Member] \| Government debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments - available for sale	0	0
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains, individually	13,000	21,000
Unrealized gains, aggregate	46,000	148,000
Unrealized losses, individually	14,000	35,000
Unrealized losses, aggregate	$ 150,000	$ 94,000

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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