Summary of Significant Accounting Policies - Concentrations of Risk - Accounts Receivable (Details) - Accounts Receivable - Credit Concentration Risk |
3 Months Ended | 12 Months Ended |
|---|---|---|
Mar. 31, 2018 |
Dec. 31, 2017 |
|
| Channel Partner, One | ||
| Accounts receivable, net | ||
| Concentration risk (as a percent) | 23.50% | 20.20% |
| Channel Partner, Two | ||
| Accounts receivable, net | ||
| Concentration risk (as a percent) | 14.80% | 16.20% |