Revenue from Contracts with Customers (Narrative) (Details 1) - Gilead Sciences Incorporation [Member] $ in Millions	Dec. 31, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expect to recognize deferred research and development revenue	$ 28.7
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expect to recognize deferred research and development revenue	$ 27.7
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year