Summary of Significant Accounting Policies Concentration of Credit Risk (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Concentration of Credit Risk [Abstract]
Disclosure On Geographic Areas Revenue From External Customers Attributed to France	82.00%	99.00%	99.00%
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile, Percent	18.00%	1.00%	1.00%