Share-based payments - Summary of the Restricted Common Stock Award (Details) - Restricted stock	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Units
Nonvested balance at beginning of period (in shares) | shares	53,389
Granted (in shares) | shares	18,673
Vested (in shares) | shares	(52,738)
Forfeited (in shares) | shares	(651)
Nonvested balance at end of period (in shares) | shares	18,673
Weighted-Average Exercise Price ($)
Nonvested balance at beginning of period (in usd per share) | $ / shares	$ 40.60
Granted (in usd per share) | $ / shares	32.83
Vested (in usd per share) | $ / shares	40.55
Forfeited (in usd per share) | $ / shares	44.13
Nonvested balance at end of period (in usd per share) | $ / shares	$ 32.83