Summary of Significant Accounting Policies - Property and Equipment Useful Lives (Details) |
12 Months Ended |
|---|---|
Dec. 31, 2017 | |
| Laboratory equipment | Maximum | |
| Property, Plant and Equipment [Line Items] | |
| Property and equipment, estimated useful lives (in years) | 8 years |
| Laboratory equipment | Minimum | |
| Property, Plant and Equipment [Line Items] | |
| Property and equipment, estimated useful lives (in years) | 4 years |
| Software, office and computer equipment | |
| Property, Plant and Equipment [Line Items] | |
| Property and equipment, estimated useful lives (in years) | 3 years |
| Furniture, fixtures and fittings | Maximum | |
| Property, Plant and Equipment [Line Items] | |
| Property and equipment, estimated useful lives (in years) | 10 years |
| Furniture, fixtures and fittings | Minimum | |
| Property, Plant and Equipment [Line Items] | |
| Property and equipment, estimated useful lives (in years) | 5 years |