Leases - Additional Information (Detail) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2019 ft²	Jun. 30, 2019 ft²	Sep. 30, 2019 USD ($) ft²	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) ft²	Sep. 30, 2018 USD ($)	Jan. 01, 2019 USD ($)
Leases [Line Items]
Office and laboratory space | ft²	11,237		36,309		36,309
Lease expiration date	Feb. 28, 2022	Jun. 30, 2023			Jun. 30, 2020
Operating lease, right-of-use assets			$ 11,372		$ 11,372		$ 3,100
Lease liability			11,863		11,863		$ 3,500
Rent expenses			$ 800	$ 600	$ 2,300	$ 1,700
2019 Sublease
Leases [Line Items]
Rentable office space under sublease | ft²		4,422
Sublease commencement date		Jun. 21, 2019
Sublease expiration date		Jun. 20, 2020