Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued Liabilities, Current [Abstract]
Accrued compensation costs	$ 1,573	$ 2,635
Accrued retention payments	2,517	795
Accrued restructuring costs	128	981
Accrued professional services	594	904
Accrued external research and manufacturing costs	1,095	1,717
Other accrued expenses	530	432
Total accrued expenses	$ 6,437	$ 7,464