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Summary of Significant Accounting Policies - Additional Information (Detail) | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2020 USD ($) Segment | Apr. 01, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jan. 01, 2019 USD ($) | Jan. 01, 2018 USD ($)
Accounting Policy [Line Items] |  |  |  |  |
Number of operating segment | Segment | 1 |  |  |  |
Currency translation adjustment |  | $ 1,300,000 |  |  |
Highly liquid investment maturity period | three months or less |  |  |  |
Restricted time deposits | $ 2,072,000 |  | $ 2,072,000 |  |
Cash and cash equivalents | $ 678,393,000 |  | 126,266,000 |  |
Short term investments maturity | 12 months |  |  |  |
Long term Investments Maturity | 12 months |  |  |  |
Impairment of long-lived assets | $ 0 |  |  |  |
Description of payment term | The period between the transfer of control of the promised goods and when the Company receives payment is based on a general 60-day payment term. |  |  |  |
Description of sales return | Distributors can request to return product to the Company only due to quality issues or for product purchased within one year prior to the product’s expiration date |  |  |  |
Accumulated deficit | $ (974,011,000) |  | (784,720,000) |  |
Accumulated other comprehensive loss | (4,499,000) |  | (747,000) |  |
ASU 2018-02 [Member] | Impact of change in accounting principle upon adoption of ASU 2018-02 [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Accumulated deficit |  |  |  | $ 600,000 |
Accumulated other comprehensive loss |  |  |  | (600,000) |
ASU 2016-01 [Member] | Impact of change in accounting principle upon adoption of ASU 2016-01 [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Accumulated deficit |  |  |  |  | $ (1,300,000)
Accumulated other comprehensive loss |  |  |  |  | $ 1,300,000
Cumulative Effect, Period of Adoption, Adjustment [Member] | ASU 2016-02 [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Accumulated deficit |  |  |  | $ (8,700,000) |
Europe [Member] | Astellas Agreement [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Amount constrained related to drug product shipment | $ 6,000,000.0 |  |  |  |
Minimum [Member] | Computer Equipment [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 3 years |  |  |  |
Minimum [Member] | Laboratory Equipment [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 3 years |  |  |  |
Minimum [Member] | Machinery [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 3 years |  |  |  |
Minimum [Member] | Furniture and Fixtures [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 3 years |  |  |  |
Maximum [Member] | Computer Equipment [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 5 years |  |  |  |
Maximum [Member] | Laboratory Equipment [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 5 years |  |  |  |
Maximum [Member] | Machinery [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 5 years |  |  |  |
Maximum [Member] | Furniture and Fixtures [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Property and equipment estimated useful life | 5 years |  |  |  |
Foreign subsidiaries [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Cash and cash equivalents | $ 66,000,000.0 |  | $ 11,900,000 |  |
Accounts Receivable from Distributors [Member] | Credit Concentration Risk [Member] |  |  |  |  |
Accounting Policy [Line Items] |  |  |  |  |
Concentration risk, percentage | 64.00% |  |  |  |

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