Commitments and Contingencies - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Nov. 30, 2017 USD ($) ft²	May 31, 2016 ft²
Commitments And Contingencies [Line Items]
Total commitment	$ 22,309,000		$ 22,309,000
Indemnification Agreement
Commitments And Contingencies [Line Items]
Accrued liabilities for indemnification agreements	0		0		$ 0
Legal Proceedings
Commitments And Contingencies [Line Items]
Expenses incurred for legal proceedings	0	$ 0	0	$ 0
Cambridge, Massachusetts | Commitment for Office and Laboratory Space Lease of Prior Corporate Headquarters
Commitments And Contingencies [Line Items]
Square feet of office and laboratory space leased under operating lease | ft²							8,143
Rent expense				100,000
Cambridge, Massachusetts | Commitment for Office and Laboratory Space Lease of Current Corporate Headquarters
Commitments And Contingencies [Line Items]
Square feet of office and laboratory space leased under operating lease | ft²						28,731
Rent expense	$ 500,000	$ 500,000	$ 1,400,000	$ 1,400,000
Total commitment						$ 25,100,000
Operating lease term						10 years
Letters of credit						$ 1,100,000