Leases - Operating Leases - Summer Street Lease (Details) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 11, 2019 ft²	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Operating leases
Restricted cash, noncurrent		$ 971		$ 971		$ 971
Weighted-average discount rate of operating leases (as a percent)		5.80%	5.30%	5.80%	5.30%
Operating lease right-of-use assets		$ 17,156		$ 17,156		17,743
Operating lease liability		23,821		23,821
Operating lease cost		633	$ 3,155	1,266	$ 7,680
Summer Street Lease
Operating leases
Option to extend the term of the lease	true
Rentable area leased (in square feet) | ft²	39,000
Operating lease, renewal term	5 years
Annual rent escalation (as a percent)	2.00%
Restricted cash, noncurrent		$ 1,000		$ 1,000
Weighted-average discount rate of operating leases (as a percent)		5.80%		5.80%
Operating lease right-of-use assets		$ 17,200		$ 17,200		17,700
Operating lease liability		23,500		23,500		$ 22,800
Operating lease cost		$ 700	$ 200	$ 1,300	$ 200