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% |