| Quarterly Financial Data (Unaudited) | 
| (14) | Quarterly Financial Data (unaudited)   |    
|   |   | Three months ended |   |  
|   |   | December 31, 2020 |   |   | September 30, 2020 |   |   | June 30, 2020 |   |   | March 31, 2020 |   |  
| Revenue |   | $ | — |   |   | $ | — |   |   | $ | — |   |   | $ | — |   |  
| Total operating expenses |   |   | (4,644 | ) |   |   | (6,335 | ) |   |   | (8,253 | ) |   |   | (12,894 | ) |  
| Net loss and comprehensive loss |   |   | (11,186 | ) |   |   | (12,199 | ) |   |   | (12,521 | ) |   |   | (16,100 | ) |  
| Net loss attributable to ordinary shareholders |   |   | (11,186 | ) |   |   | (12,199 | ) |   |   | (12,521 | ) |   |   | (16,100 | ) |  
| Net loss per share attributable to ordinary shareholders – basic and diluted |   | $ | (0.28 | ) |   | $ | (0.60 | ) |   | $ | (0.80 | ) |   | $ | (1.08 | ) |  
| Weighted average ordinary shares outstanding – basic and diluted |   |   | 40,645,864 |   |   |   | 20,392,357 |   |   |   | 15,614,767 |   |   |   | 14,868,973 |   |    
|   |   | Three months ended |   |  
|   |   | December 31, 2019 |   |   | September 30, 2019 |   |   | June 30, 2019 |   |   | March 31, 2019 |   |  
| Revenue |   | $ | — |   |   | $ | — |   |   | $ | — |   |   | $ | 37 |   |  
| Total operating expenses |   |   | (23,178 | ) |   |   | (30,999 | ) |   |   | (27,378 | ) |   |   | (20,503 | ) |  
| Net loss and comprehensive loss |   |   | (23,641 | ) |   |   | (31,271 | ) |   |   | (27,638 | ) |   |   | (20,580 | ) |  
| Net loss attributable to ordinary shareholders |   |   | (23,641 | ) |   |   | (31,271 | ) |   |   | (27,638 | ) |   |   | (20,580 | ) |  
| Net loss per share attributable to ordinary shareholders – basic and diluted |   | $ | (1.59 | ) |   | $ | (2.15 | ) |   | $ | (1.93 | ) |   | $ | (1.44 | ) |  
| Weighted average ordinary shares outstanding – basic and diluted |   |   | 14,866,838 |   |   |   | 14,571,278 |   |   |   | 14,340,231 |   |   |   | 14,290,437 |   |    |