Income Taxes (Schedule of Deferred Taxes) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Abstract]
Federal and state net operating loss carryforwards	$ 30,350	$ 28,399
Research and development tax credit carryforwards	2,438	2,338
Stock based compensation	1,470	1,674
Other provision and expenses not currently deductible	1,345	877
Total deferred tax assets	35,603	33,288
Depreciation and amortization	(726)	(721)
Prepaid expenses	(151)	(94)
Total deferred liabilities	(877)	(815)
Less valuation allowance	(34,726)	(32,473)
Net deferred tax asset