Share-based compensation - PSU activity (Details) - $ / shares	1 Months Ended		9 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Sep. 30, 2022
Other disclosure
Service period	3 years	1 year
Performance Share Awards | 2014 Plan
Number of shares
Non-vested at beginning of period (in shares)			632,930
Granted (in shares)			34,700
Vested (in shares)			(103,970)
Forfeited (in shares)			(48,800)
Non-vested at end of period (in shares)	632,930		514,860
Weighted average grant-date fair value
Non-vested at beginning of period (in dollars per share)			$ 33.54
Granted (in dollars per share)			15.11
Vested (in dollars per share)			52.14
Forfeited (in dollars per share)			29.35
Non-vested at end of period (in dollars per share)	$ 33.54		$ 28.94