Other Financial Information - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Other Financial Information [Abstract]
Supplier advances	$ 188	$ 73
Interest receivable	388	272
Other prepaid expenses and current assets	1,087	966
Total prepaid expenses and other current assets	$ 1,663	$ 1,311