Income Taxes (Significant Components of Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Deferred royalty obligation	$ 31,937	$ 0
Stock-based compensation	11,904	6,744
Depreciation and amortization	1,033	511
Other	1,004	124
Deferred Tax Assets, Gross	45,878	7,379
Valuation allowance	(45,878)	(7,379)
Net deferred tax assets	$ 0	$ 0