Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Accrued Expenses and Other Current Liabilities
Accrued salaries and benefits	$ 437	$ 506
Accrued severance and other charges	0	28
Accrued warranty	76	125	$ 65	$ 338
Warrant liability	78	669
Other	349	211
Accrued expenses and other current liabilities	$ 940	$ 1,539