Income Taxes (Significant Components of Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Federal and state net operating losses	$ 7,391	$ 23,551
Capitalized research and patent costs	7,317	10,260
Research credits	26,164	24,771
Stock-based compensation costs	12,026	9,124
Operating lease liability	857	0
Other	4,186	6,137
Total deferred tax assets	57,941	73,843
Operating lease right-of-use asset	(11,410)	(11,184)
Deferred tax liabilities
Operating lease right-of-use asset	(854)	0
Total deferred tax liabilities	(854)	0
Net deferred tax assets	$ 45,677	$ 62,659