Accrued Expenses and Other Liabilities - Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Components of accrued expenses and other current liabilities:
Research and development related costs	$ 4,487	$ 8,716
Payroll and related costs	3,520	2,150
Accounting, tax and audit services	222	484
Other	2,785	1,976
Total other current liabilities	$ 11,014	$ 13,326