Description of the Business and Summary of Significant Accounting Policies (Short-term Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Short Term Investments [Line Items]
Short-term investments	$ 262,174	$ 228,783
Certificates of Deposit [Member]
Short Term Investments [Line Items]
Short-term investments	41,100	130,000
Commercial Paper [Member]
Short Term Investments [Line Items]
Short-term investments	$ 221,100	59,200
US Treasury Securities [Member]
Short Term Investments [Line Items]
Short-term investments		$ 39,600