Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued Expenses
Employee compensation expenses	$ 4,219	$ 3,010
Sales and marketing expenses	833	39
Research and development expenses	1,900	627
Capital leases, current portion	591	142
Professional fees	336	108
Payable to NST		590
Other	666	424
Total accrued expenses	$ 8,545	$ 4,940