Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Accrued Expenses and Other Current Liabilities
Accrued salaries and benefits	$ 790	$ 759
Accrued severance and other charges	400	1,738
Accrued warranty	312	338	$ 244	$ 228
Warrant liability	1,560	1,226
Liability for consigned precious metals	1,615	1,282
Other	466	1,002
Accrued expenses and other current liabilities	$ 5,143	$ 6,345