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Investments - Summary of Gross Unrealized Losses and Fair Value of Available-For-Sale Investment Securities in Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	$ 257,337	$ 169,353
Less Than 12 Months, Unrealized Losses	(40)	(43)
Total, Estimated Fair Value	257,337	169,353
Total, Unrealized Losses	(40)	(43)
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	105,515	129,631
Less Than 12 Months, Unrealized Losses	(11)	(27)
Total, Estimated Fair Value	105,515	129,631
Total, Unrealized Losses	(11)	(27)
US Government Sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	56,012	10,004
Less Than 12 Months, Unrealized Losses	(6)	(5)
Total, Estimated Fair Value	56,012	10,004
Total, Unrealized Losses	(6)	(5)
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	76,688	23,466
Less Than 12 Months, Unrealized Losses	(16)	(11)
Total, Estimated Fair Value	76,688	23,466
Total, Unrealized Losses	(16)	(11)
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value	19,122
Less Than 12 Months, Unrealized Losses	(7)
Total, Estimated Fair Value	19,122
Total, Unrealized Losses	$ (7)
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Estimated Fair Value		6,252
Total, Estimated Fair Value		$ 6,252

X

- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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