Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued expenses and other liabilities
Research and development related costs	$ 3,026	$ 5,032
Payroll and related costs	4,665	7,427
Accounting, tax and audit services	209	398
Other	2,633	1,645
Total other current liabilities	$ 10,533	$ 14,502