Leases - Additional Information (Detail) $ in Thousands		3 Months Ended		6 Months Ended
	Aug. 15, 2019 USD ($) RenewalOption	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 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		$ 17,183		$ 17,183
Operating lease liability		10,500		10,500		$ 10,600
Operating lease right-of-use asset		7,861		7,861		$ 8,054
Operating lease expense		$ 500	$ 400	$ 1,000	$ 800
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