Income Taxes (Reconciliation of the provision for income taxes at the statutory rate to the company's provision for income tax) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal (tax benefit) provision at statutory rate	$ (3,772)	$ (2,105)	$ (4,576)
State (tax benefit) income taxes, net of federal benefit	(646)	(373)	(437)
Foreign income taxes at rates other than the US rate	(145)	92	(21)
Stock-based compensation	(2,119)	(3,503)	(8,373)
Change in valuation allowance	5,136	4,710	(6,023)
Non-deductible executive compensation	2,383	2,418	1,624
Rate differential impact on Tax Cuts and Jobs Act	0	0	18,975
Research and development credits	(1,209)	(994)	(602)
Indefinite net operating losses carryforward	(33)
Other	425	874	192
Total income tax provision (benefit)	$ 20	$ (351)	$ 759
Effective Income Tax Rate, Percent [Abstract]
Effective tax rate	0.10%	(3.50%)	7.50%