Description of Business and Summary of Significant Accounting Policies (Concentrations of Risk) (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
|
| Segment Reporting | ||
| Revenue concentration | $ 0 | $ 0 |
| Concentration risk, percentage | 10.00% | 10.00% |