Income Taxes (Schedule of Deferred Taxes) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Abstract]
Federal and state net operating loss carryforwards	$ 30,428	$ 30,350
Research and development tax credit carryforwards	2,479	2,438
Stock based compensation	1,632	1,470
Other provision and expenses not currently deductible	1,327	1,345
Total deferred tax assets	35,866	35,603
Depreciation and amortization	(693)	(726)
Prepaid expenses	(195)	(151)
Total deferred liabilities	(888)	(877)
Less valuation allowance	(34,978)	(34,726)
Net deferred tax asset