Commitments and Contingencies - Additional Information (Details)	1 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($) ft²	Sep. 30, 2016	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commitment And Contingencies [Line Items]
Deferred rent incentives			$ 8,300,000
Rent expense, net			1,400,000	$ 2,700,000
Letters Of Credit And Secured By Restricted Cash
Commitment And Contingencies [Line Items]
Security deposit			1,300,000	1,800,000
Maximum
Commitment And Contingencies [Line Items]
Tenant improvement allowance			$ 10,900,000
Bedford, Massachusetts
Commitment And Contingencies [Line Items]
Operating lease beginning year and month		2016-11
Operating lease expiration year and month	2027-02	2021-10
Operating lease agreements additional term		3 years
Sublease aggregate base rent obligation				$ 2,700,000
Office space leased | ft²	67,000
Lessee, operating lease, lease not yet commenced, renewal term	5 years
Initial annual base rent per square foot	$ 39.50
Percentage increase in initial annual base rent per square foot.	3.00%