Leases - Additional Information (Detail) $ in Thousands					3 Months Ended
	Aug. 15, 2019 USD ($) RenewalOption	Jan. 26, 2019	Sep. 30, 2011	Jul. 01, 2011	Mar. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Incremental borrowing rate for purposes of calculation of lease liabilities					11.50%
Change in incremental borrwing rate					1.00%
Short-term lease commited aggregate payment amount					$ 300
Monthly rent payment					18,224
Operating lease liability					9,000
Current operating lease liability					$ 1,095
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]					amrn:AccruedLiabilitiesAndOtherLiabilitiesCurrent
Operating lease right-of-use asset					$ 8,900
Operating lease expense					$ 300
Dublin
Lessee Lease Description [Line Items]
Operating lease, expiration date			Oct. 31, 2019
Bedminster
Lessee Lease Description [Line Items]
Operating lease, expiration date		Jun. 30, 2019		Sep. 15, 2019
Bridgewater
Lessee Lease Description [Line Items]
Description of lease agreement					Amarin will have a one-time option to terminate the agreement effective on the first day of the ninety-seventh 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 ninety-seventh month after the Commencement Date
Bridgewater | Scenario Forecast
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
Lease termination existence of option to extend	true
Monthly rent payment	$ 100
Maximum
Lessee Lease Description [Line Items]
Short term lease period					12 months