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Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Income Taxes [Line Items] |  |  |
Deferred tax assets, valuation allowance | $ 346,000 | $ 335,200 |
Research and development tax credit carry forwards | $ 71,900 | 62,200 |
Percentage of uncertain tax positions likelihood of being sustained | 50.00% |  |
Increases related to current year tax positions | $ 9,519 | $ 11,726 | $ 3,291
Unrecognized tax benefits that would affect effective tax rate | 57,900 |  |
Federal |  |  |
Income Taxes [Line Items] |  |  |
Operating loss carry forward, net | $ 816,200 |  |
Operating loss carry forward beginning expiration year | 2024 |  |
Research and development tax credit carry forwards | $ 73,200 |  |
Federal | R&D |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carry forwards beginning expiration year | 2019 |  |
State and Local Jurisdiction |  |  |
Income Taxes [Line Items] |  |  |
Operating loss carry forward, net | $ 359,800 |  |
Research and development tax credit carry forwards | $ 47,500 |  |
State and Local Jurisdiction | California |  |  |
Income Taxes [Line Items] |  |  |
Operating loss carry forward beginning expiration year | 2028 |  |
State and Local Jurisdiction | Other States |  |  |
Income Taxes [Line Items] |  |  |
Operating loss carry forward beginning expiration year | 2026 |  |

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