Quarterly report pursuant to Section 13 or 15(d)

Share-based compensation - Options (Details)

v3.8.0.1
Share-based compensation - Options (Details)
3 Months Ended
Mar. 31, 2018
$ / shares
shares
Mar. 31, 2018
£ / shares
shares
Mar. 31, 2017
$ / shares
shares
Number of options granted (in shares) | shares 9,994,656 9,994,656 18,950,976
Weighted average fair value (in dollars per share) | $ / shares $ 0.75   $ 0.34
RSU      
Number of options granted (in shares) | shares 6,552,636 6,552,636  
Weighted average fair value (in dollars per share) | $ / shares $ 1.34    
Exercise price | £ / shares   £ 0.001  
Vesting period (in years) 4 years 4 years  
Contractual term (in years) 10 years 10 years  
First anniversary | RSU      
Vesting percentage (as a percent) 25.00% 25.00%  
Annual installments over the following three years | RSU      
Vesting percentage (as a percent) 75.00% 75.00%