Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Accrued Expenses and Other Current Liabilities
Accrued salaries and benefits	$ 526	$ 759
Accrued severance and other charges	392	1,738
Accrued warranty	65	338	$ 314	$ 228
Warrant liability	788	1,226
Liability for consigned precious metals	1,695	1,282
Other	506	1,002
Accrued expenses and other current liabilities	$ 3,972	$ 6,345