Annual report pursuant to Section 13 and 15(d)

Share-based compensation - Fair Value Assumptions (Details)

v3.8.0.1
Share-based compensation - Fair Value Assumptions (Details) - company
7 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2015
Assumptions used to estimate the fair values of the share options granted using the Black-Scholes option-pricing model        
Expected term (in years)   5 years 5 years 5 years
Expected volatility, minimum (as a percent)   66.00% 68.00%  
Expected volatility (as a percent)       60.00%
Expected volatility, maximum (as a percent)   71.00% 73.00%  
Risk free rate, minimum (as a percent)   0.40% 0.17% 1.04%
Risk free rate, maximum (as a percent)   0.76% 1.07% 1.54%
Expected dividend yield (as a percent)   0.00% 0.00% 0.00%
Number of companies with similar attributes, considered for expected volatility rate computation   7    
Volatility of the share price determine period 2 years