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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 | Dec. 31, 2020 | Dec. 31, 2019
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Schedule of Available-for-sale Securities [Line Items] |  |
Less Than 12 Months, Estimated Fair Value | $ 169,353 | $ 220,834
Less Than 12 Months, Unrealized Losses | (43) | (51)
Total, Estimated Fair Value | 169,353 | 220,834
Total, Unrealized Losses | (43) | (51)
US Treasury Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less Than 12 Months, Estimated Fair Value | 129,631 | 148,397
Less Than 12 Months, Unrealized Losses | (27) | (13)
Total, Estimated Fair Value | 129,631 | 148,397
Total, Unrealized Losses | (27) | (13)
Corporate debt securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less Than 12 Months, Estimated Fair Value | 6,252 | 11,334
Less Than 12 Months, Unrealized Losses |  | (8)
Total, Estimated Fair Value | 6,252 | 11,334
Total, Unrealized Losses |  | (8)
US Government Sponsored Enterprises Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less Than 12 Months, Estimated Fair Value | 10,004 | 61,103
Less Than 12 Months, Unrealized Losses | (5) | (30)
Total, Estimated Fair Value | 10,004 | 61,103
Total, Unrealized Losses | (5) | $ (30)
Commercial paper |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less Than 12 Months, Estimated Fair Value | 23,466 |
Less Than 12 Months, Unrealized Losses | (11) |
Total, Estimated Fair Value | 23,466 |
Total, Unrealized Losses | $ (11) |

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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=121645371&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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