Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets, Gross [Abstract]
NOL and credit carryforwards	$ 75,063,000	$ 64,486,000
Compensation accruals	4,542,000	4,143,000
Accruals and reserves	1,401,000	2,207,000
State tax provision	7,000	5,000
Inventory adjustments	1,193,000	1,329,000
Intangible assets	498,000	455,000
Other	620,000	65,000
Gross deferred tax assets	83,324,000	72,690,000
Less: valuation allowance	(81,964,000)	(71,464,000)
Total deferred tax assets	1,360,000	1,226,000
Deferred Tax Liabilities, Net [Abstract]
Depreciation	1,102,000	1,226,000
Contract acquisition costs	258,000	0
Total deferred tax liabilities	1,360,000	1,226,000
Net deferred tax assets (liabilities)	$ 0	$ 0