Leases - Additional Information (Details) $ in Thousands		3 Months Ended	6 Months Ended
	Mar. 12, 2019 USD ($) ft²	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 30, 2018 USD ($) ft²
Land Subject to Ground Leases | ft²	1,038
Lessee Operating Lease Monthly Average Rental Payment	$ 2
Operating Lease, Payments			$ 400
Total rent expense		$ 200		$ 400
Security Deposit			2
Operating Lease, Right-of-Use Asset			1,438
Operating Lease, Liability			1,438
Boston, MA
Security Deposit			$ 100			$ 100
Sublease term amendment			Aug. 31, 2021
Operating lease expiration month and year			2016-08
Houston, TX
Operating Lease Area | ft²							210
Operating Leases Future Minimum Monthly Payment Due Through Year 2021							$ 1
Adjustments for New Accounting Pronouncement [Member]
Operating Lease, Right-of-Use Asset					$ 1,600
Operating Lease, Liability					$ 1,600