Income Taxes (Reconciliation of Federal Statutory Income Tax Rate to Effective Income Tax Rate) (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. federal statutory tax rate	21.00%	21.00%	35.00%
Foreign income taxed at different rates	(5.60%)	(4.90%)	(14.20%)
Effect of the Tax Act
Transition tax	(0.006)	(0.001)	0.376
Deferred tax effects	0.00%	(1.20%)	(1.40%)
Federal research credit	(2.50%)	(2.40%)	(1.80%)
Stock-based compensation expense	(0.70%)	(2.20%)	(4.50%)
European Commission fines	1.00%	3.10%	3.50%
Deferred tax asset valuation allowance	0.00%	(2.00%)	0.90%
State and local income taxes	1.10%	(0.40%)	0.10%
Other adjustments	(0.40%)	1.10%	(1.80%)
Effective tax rate	13.30%	12.00%	53.40%