Summary of Significant Accounting Policies - Concentrations of Risk - Revenue (Details) - Customer Concentration Risk - Sales Revenue, Services, Net |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Revenue: | ||
| Concentration risk (as a percent) | 27.00% | |
| Channel Partner, One | ||
| Revenue: | ||
| Concentration risk (as a percent) | 23.10% | |
| Channel Partner, Two | ||
| Revenue: | ||
| Concentration risk (as a percent) | 16.10% | |