Income Taxes (Significant Components of Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Federal and state net operating losses	$ 23,551	$ 41,902
Capitalized research and patent costs	10,260	13,278
Research credits	24,771	22,606
Stock-based compensation costs	9,124	5,596
Other	6,137	5,795
Total deferred tax assets	73,843	89,177
Valuation allowance	(11,184)	(12,474)
Net deferred tax assets	$ 62,659	$ 76,703