Basic and diluted earnings per share (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Basic and diluted earnings per share
Total potential dilutive ordinary shares	11,600,123	12,236,211
BMS Warrants | Bristol Myers Squibb
Basic and diluted earnings per share
Total potential dilutive ordinary shares	8,060,500	8,435,000
Stock options | 2014 Plan
Basic and diluted earnings per share
Total potential dilutive ordinary shares	2,879,733	2,943,756
Stock options | Previous option plan
Basic and diluted earnings per share
Total potential dilutive ordinary shares	14,000	14,000
Stock options | ESPP
Basic and diluted earnings per share
Total potential dilutive ordinary shares	254	596
Non-vested and earned RSUs and PSUs
Basic and diluted earnings per share
Total potential dilutive ordinary shares	645,636	842,859