Leases - Additional Information (Details) € in Millions		1 Months Ended						12 Months Ended			22 Months Ended
	Sep. 21, 2015 USD ($) ft² $ / ft²	Sep. 30, 2020 ft² $ / ft²	Jul. 31, 2020 USD ($)	Mar. 31, 2020 EUR (€)	Sep. 30, 2019 ft² lease_term $ / ft²	Apr. 30, 2019 USD ($) ft² $ / ft²	Jul. 31, 2018 ft² $ / ft²	Dec. 31, 2020 USD ($) lease_term	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Nov. 30, 2016	Jun. 03, 2016
Lessee, Lease, Description [Line Items]
lease arrangements annual rent increase percentage						3.00%
Operating lease, expense								$ 47,700,000	$ 45,300,000
Rent expense										$ 9,800,000
Seattle, Washington
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) | ft²		22,188			22,188		36,126
Annual lease rent per square foot (in dollars per sq ft) | $ / ft²		62.80			62.80		54.00
Lease rent, annual increase percentage		2.50%			2.50%		2.50%
Lease extension terms					5 years
Lessee, operating lease, term of contract extension					16 months
Lessee, operating lease, number of contracts | lease_term					2
60 Binney Street lease
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) | ft²	253,108
Annual lease rent per square foot (in dollars per sq ft) | $ / ft²	72.50
Lease payments base annual rent	$ 18,400,000
Lease rent, annual increase percentage	1.75%
Collateralized letter of credit	$ 13,800,000
Decrease In letter of credit under the terms of the lease	9,200,000
Landlord contribution for cost of construction and tenant improvements	$ 42,400,000
Lessee, operating lease, number of terms | lease_term								2
Lease extension terms								5 years
50 Binney Street sublease
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) | ft²						267,278
Collateralized letter of credit						$ 40,100,000
Rate of area for sublease per square feet (in dollars per sq ft) | $ / ft²						99.95
Lessee, operating lease, annual expense						$ 26,700,000
Lessee, operating sublease, payment commencement, term						90 days
Upfront payment for purchase of furniture and equipment						$ 7,500,000
Manufacturing Facility
Lessee, Lease, Description [Line Items]
Lease extension terms												3 years
Lessee, operating lease, annual expense								$ 5,100,000
Lease period			5 years									5 years	12 years
Milestone paid											$ 12,000,000.0
Lessee, operating lease, termination fees, term								24 months
Lessee, operating lease, maximum potential annual maintenance and production fees | €				€ 16.5
Lessee, operating lease, termination notice period			18 months	12 months
Lessee, operating lease, maximum potential annual maintenance fees			$ 5,400,000