Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Components of accrued expenses and other current liabilities:
Research and development related costs	$ 2,479	$ 2,308
Payroll and related costs	2,651	4,426
Accounting, tax and audit services	586	231
Other	1,861	1,159
Total other current liabilities	$ 7,577	$ 8,124