Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Components of accrued expenses and other current liabilities:
Research and development related costs	$ 2,695	$ 2,308
Payroll and related costs	3,760	4,426
Accounting, tax and audit services	182	231
Other	1,727	1,159
Total other current liabilities	$ 8,364	$ 8,124