Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share	37,361,469	32,819,830
Foreign currency translation adjustment	$ 9,600		$ 11,800
Restricted Cash and Cash Equivalents	30,188		30,314
Security Deposit [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents	1,700		1,700
Grant Agreement [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents	$ 45,700		$ 33,200
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