Leases - Additional Information (Details) $ in Thousands		3 Months Ended
	Mar. 12, 2019 USD ($) ft²	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)	Jan. 30, 2018 USD ($) ft²
Land Subject to Ground Leases | ft²	1,038
Lessee Operating Lease Monthly Average Rental Payment	$ 2
Operating Lease, Payments		$ 178
Operating Leases, Rent Expense, Net			$ 178
Security Deposit		2
Operating Lease, Right-of-Use Asset		1,589
Operating Lease, Liability		1,592
Boston, MA
Security Deposit		$ 128	$ 128
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