Summary of Significant Accounting Policies Narrative (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
Dec. 31, 2016 |
|
| Accounting Policies [Abstract] | |||||
| Advertising costs | $ 1.2 | $ 0.8 | $ 3.3 | $ 1.9 | |
| Deferred equity offering costs | $ 2.9 | $ 2.9 | $ 1.0 | ||