Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Sep. 30, 2015	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share		61,260,970	45,126,499
Foreign currency translation adjustment		$ 12,400			$ 11,200
Restricted cash current		6,628			10,847
Operating Lease, Liability		20,887
Lessor, Operating Lease, Term of Contract				12 months
Accounting Standards Update 2016-02 [Member]
Summary of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset				$ 12,000
Operating Lease, Liability				$ 22,000
Bill Melinda Gates Foundation [Member]
Summary of Significant Accounting Policies [Line Items]
Grant Agreement	$ 89,100	89,100
Security Deposit [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted cash current		1,000			1,000
Grant Agreement [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted cash current		$ 7,500			$ 10,800
Convertible Debt Securities [Member]
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share		47,716,900
Convertible Notes Initial Conversion Price Per Share		$ 6.81