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Gross Amounts and Dates of Expiration of Tax Credits and Carryovers (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Income Tax Disclosure [Line Items] |  |
Federal losses carryovers | $ 638,103 |
California loss carryovers | 75,407 |
Research credits | 28,892 | $ 28,291
Federal foreign tax credits | 610 |
Federal |  |
Income Tax Disclosure [Line Items] |  |
Research credits | 19,249 |
California |  |
Income Tax Disclosure [Line Items] |  |
Research credits | 12,207 |
Expires 2021-2023 |  |
Income Tax Disclosure [Line Items] |  |
Federal losses carryovers | 55,587 |
Expires 2021-2023 | Federal |  |
Income Tax Disclosure [Line Items] |  |
Research credits | 7,786 |
Expires 2024-2030 |  |
Income Tax Disclosure [Line Items] |  |
Federal losses carryovers | 190,581 |
California loss carryovers | 28,779 |
Federal foreign tax credits | 610 |
Expires 2024-2030 | Federal |  |
Income Tax Disclosure [Line Items] |  |
Research credits | 2,248 |
Expires 2031-2040 |  |
Income Tax Disclosure [Line Items] |  |
Federal losses carryovers | 209,368 |
California loss carryovers | 46,628 |
Expires 2031-2040 | Federal |  |
Income Tax Disclosure [Line Items] |  |
Research credits | 9,215 |
No Expiration |  |
Income Tax Disclosure [Line Items] |  |
Federal losses carryovers | 182,567 |
No Expiration | California |  |
Income Tax Disclosure [Line Items] |  |
Research credits | $ 12,207 |

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