8. Income Taxes (Details 2) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Operating loss carryforwards	$ 1,874	$ 1,035
R&D tax credit	1,478	1,310
AMT tax credit	352	364
Section 263A costs	315	502
R&D costs	335	690
Amortization	24	34
Asset reserves:
Bad debts	12	18
Inventory reserve	182	574
Accrued expenses:
Non-qualified stock options	86	86
Compensation	165	261
Warranty	465	415
Deferred tax assets	5,288	5,289
Less state valuation allowance	(64)	(76)
Total deferred tax assets	5,224	5,213
Deferred tax liabilities:
Depreciation	(338)	(626)
Total deferred tax liabilities	(338)	(626)
Net deferred tax assets (before unrealized gain)	4,886	4,587
Deferred tax liability: unrealized gain	(1,569)	(1,169)
Net deferred tax assets	$ 3,317	$ 3,418