Income Taxes (Significant Components of Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating losses	$ 75,149	$ 50,144
Research and other credits	2,178	2,178
Stock based compensation	3,256	3,001
In-Process research and development	1,193	1,253
Other	665	854
Total deferred tax assets	82,441	57,430
Valuation allowance	(82,441)	(57,430)
Net deferred tax assets