Leases - Additional Information (Detail) € in Millions		1 Months Ended			3 Months Ended	22 Months Ended
	Sep. 21, 2015 USD ($) ft² $ / ft²	Sep. 30, 2019 ft² lease_term $ / ft²	Apr. 30, 2019 USD ($) ft² $ / ft²	Jul. 31, 2018 ft² $ / ft²	Mar. 31, 2020 USD ($) lease_term	Mar. 31, 2018 USD ($)	Mar. 06, 2020 EUR (€)	Nov. 18, 2016	Jun. 03, 2016
Seattle, Washington
Lessee, Lease, Description [Line Items]
Lease building space (in sq ft) | ft²		22,188		36,126
Annual lease rent per square foot (in dollars per sq ft) | $ / ft²		62.80		54.00
Renewal term		5 years
Lessee, Operating Lease, Term Of Contract Extension		16 months
Lease Arrangements Annual Increase Percentage		2.50%		2.50%
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
Number of terms | lease_term					2
Renewal term					5 years
50 Binney Street Sublease
Lessee, Lease, Description [Line Items]
Collateralized letter of credit			$ 40,100,000
Area of office space for sublease | ft²			267,278
Rate of area for sublease per square feet | $ / ft²			99.95
Annual expense			$ 26,700,000
Annual rent increase percentage			3.00%
Payment commencement, term			90 days
Upfront payment for purchase of furniture and equipment					$ 7,500,000
50 Binney Street Sublease | Minimum
Lessee, Lease, Description [Line Items]
Option to postpone commencement, term			9 months
Manufacturing Facility
Lessee, Lease, Description [Line Items]
Renewal term								3 years
Annual expense					$ 5,100,000
Lease period								5 years	12 years
Lease notice period					12 months
Milestone paid						$ 12,000,000.0
Lease not yet commenced, amount					$ 8,000,000.0
Termination fees, term					24 months
Annual maintenance and production fees | €							€ 16.5