Contractual Obligations and Commitments - Narratives (Details) $ in Millions					3 Months Ended
	May 08, 2019	Nov. 12, 2018 ft²	Aug. 15, 2018 USD ($)	Apr. 05, 2018 USD ($) ft²	Mar. 31, 2020 USD ($)
Operating Leased Assets [Line Items]
Agreement to purchase goods and services					$ 0.9
Dublin, Ireland [Member]
Operating Leased Assets [Line Items]
Lessee operating lease, lease commencement date	May 31, 2019
Initial term of lease					18 months
Operating lease, option to extend					a 12-month extension period in our right-of-use asset and lease liability
Lessee, Operating Lease, Existence of Option to Extend	true
Office Space for Corporate Headquarters [Member]
Operating Leased Assets [Line Items]
Lessee operating lease, lease commencement date				Aug. 15, 2018
Area of office space under lease agreement | ft²				30,175
Initial term of lease				123 months
Operating lease, option to extend					option to extend the lease for an additional five-year term
Term of lease extension				5 years
Tenant improvement allowance			$ 3.6
Period of free rent			3 months
Initial letter of credit to secure lease obligation				$ 2.4
Letter of credit to secure lease obligation on third anniversary of rent commencement date				1.8
Letter of credit to secure lease obligation on fifth anniversary of rent commencement date				$ 1.2
Ionis Sublease
Operating Leased Assets [Line Items]
Area of office space under lease agreement | ft²		4,723
Initial term of lease		64 months
Period of free rent		4 months
Lessee, Operating Lease, Existence of Option to Extend		false