Balance Sheet Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Accrued sales commission payable	$ 258	$ 389
Accrued manufacturing expenses	1,686	1,106
Liabilities to certain customers	2,242	4,144
Warranty reserve	504	513
Income tax payable	513	132
Deferred revenue, current portion	224	415
Interest payable	171	950
Other accrued liabilities	1,508	1,719
Total accrued expenses and other current liabilities	$ 7,106	$ 9,368