Income Taxes (Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
U.S. federal income tax rate	35.00%		35.00%	35.00%
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
United States federal tax expense (benefit) at statutory rate	$ (7,067)	$ (12,949)	$ (29,662)
State taxes, net of United States federal tax expense (benefit)	(273)	(533)	(1,240)
Change in valuation allowance	1,133	13,148	27,821
Non-deductible stock compensation	587	144	218
Impact of non-U.S. jurisdictional tax rate difference	603	335	916
Research and development tax credit	0	(338)	(243)
Increase (reversal) of unrecognized tax benefits	0	135	(1,269)
Non-U.S. withholding tax	435	452	141
Other	407	(156)	444
Total income tax expense (benefit)	$ (2,778)	$ 776	$ (1,290)