Commitments and Contingencies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) ft²	Mar. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Right-of-use asset	$ 3,001
Operating lease, liability	3,400
Rent expense	$ 125	$ 31
2016 Lease Agreement [Member]
Operating Leased Assets [Line Items]
Lease expiration date	Feb. 28, 2027
Additional area of real estate property leased | ft²	31,000
Clinical Supply Agreement [Member]
Operating Leased Assets [Line Items]
Estimated remaining commitment	$ 2,200
Project management service fee	$ 803	$ 801