Income Taxes (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended |
|---|---|---|
Mar. 31, 2018 |
Dec. 31, 2017 |
|
| Operating Loss Carryforwards [Line Items] | ||
| Unrecognized tax benefits | $ 0.0 | $ 0.0 |
| Federal tax at statutory rate (as a percent) | 21.00% | 35.00% |
| Federal | ||
| Operating Loss Carryforwards [Line Items] | ||
| Net operating loss carryforwards | $ 110.9 | |
| State | ||
| Operating Loss Carryforwards [Line Items] | ||
| Net operating loss carryforwards | 65.9 | |
| R&D credit | ||
| Operating Loss Carryforwards [Line Items] | ||
| Credit carryforwards | $ 1.4 |