Income Taxes (Significant Components of Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 81,406	$ 60,105
Research and development credits	24,011	21,262
Deferred royalty obligation	30,460	31,937
Share-based compensation expense	9,581	11,904
Depreciation and amortization expense	0	1,033
Lease liability	7,127	0
Other	1,263	1,004
Deferred Tax Assets, Gross	153,848	127,245
Depreciation and amortization	(1,612)	0
Right-of-use lease asset	(3,775)	0
Valuation allowance	(148,461)	(127,245)
Net deferred tax assets	$ 0	$ 0