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Leases - Additional Information (Detail) $ in Thousands |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Aug. 15, 2019 USD ($) RenewalOption | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Lessee Lease Description [Line Items] |  |  |  |  |  |
Incremental borrowing rate for purposes of calculation of lease liabilities |  | 11.50% |  | 11.50% |  |
Change in incremental borrowing rate |  |  |  | 1.00% |  |
Monthly rent payment |  | $ 16,817 |  | $ 16,817 |  |
Operating lease liability |  | 10,500 |  | 10,500 |  | $ 10,600
Operating lease right-of-use asset |  | 7,762 |  | 7,762 |  | $ 8,054
Operating lease expense |  | $ 500 | $ 400 | $ 1,500 | $ 1,200 |
Bridgewater |  |  |  |  |  |
Lessee Lease Description [Line Items] |  |  |  |  |  |
Lease commencement date | Aug. 15, 2019 |  |  |  |  |
Lease agreement term | 11 years |  |  |  |  |
Number of renewal options | RenewalOption | 2 |  |  |  |  |
Lease renewal term | 5 years |  |  |  |  |
Description of lease agreement |  |  |  | Amarin will have a one-time option to terminate the agreement effective on the first day of the 97th month after the Commencement Date upon advance written notice and a termination payment specified in the Lease. |  |
Lease termination description |  |  |  | one-time option to terminate the agreement effective on the first day of the 97th month after the Commencement Date |  |
Lease termination existence of option to extend | true |  |  |  |  |
Monthly rent payment | $ 100 |  |  |  |  |
Maximum |  |  |  |  |  |
Lessee Lease Description [Line Items] |  |  |  |  |  |
Short term lease period |  |  |  | 12 months |  |

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