Share-based payments (Summary of Stock Option Activity) (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Share-based payments
Outstanding beginning balance, Common shares under option | shares	2,797,189
Granted, Common shares under option | shares	772,074
Exercised, Common shares under option | shares	(679,277)
Forfeited, Common shares under option | shares	(28,651)
Expired, Common shares under option | shares	(1,201)
Outstanding ending balance, Common shares under option | shares	2,860,134	2,797,189
Exercisable, Common shares under option | shares	1,397,769
Outstanding beginning balance, Weighted average exercise price (per share) | $ / shares	$ 29.05
Granted, Weighted average exercise price (per share) | $ / shares	40.84
Exercised, Weighted average exercise price (per share) | $ / shares	28.60
Forfeited, Weighted average exercise price (per share) | $ / shares	30.55
Expired, Weighted average exercise price (per share) | $ / shares	21.82
Outstanding ending balance, Weighted average exercise price (per share) | $ / shares	32.33	$ 29.05
Exercisable, Weighted average exercise price (per share) | $ / shares	$ 27.41
Outstanding, Weighted average remaining contractual life (in years)	7 years 7 months 6 days	7 years 1 month 6 days
Exercisable, Weighted average remaining contractual life (in years)	6 years 1 month 6 days
Outstanding beginning balance, Aggregate intrinsic value | $	$ 38,874
Exercised, Aggregate intrinsic value | $	9,600
Outstanding ending balance, Aggregate intrinsic value | $	24,496	$ 38,874
Exercisable, Aggregate intrinsic value | $	$ 18,785