Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share	44,837,650	37,361,469
Foreign currency translation adjustment	$ 11,200		$ 8,600
Restricted Cash and Cash Equivalents	10,132		28,234
Security Deposit [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents	1,000		1,700
Grant Agreement [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents	$ 10,100		$ 27,400
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