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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
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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

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- 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 + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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- Definition 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. + References No definition available. + Details
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