Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accrued Expenses
Employee compensation expenses	$ 3,922	$ 3,010
Sales and marketing expenses	1,237	39
Research and development expenses	938	627
Capital leases, current portion	552	142
Professional fees	389	108
Payable to NST		590
Other	527	424
Total accrued expenses	$ 7,565	$ 4,940