Share-based payments - Summary of Restricted Common Stock Unit Activity (Details) - Restricted stock unit	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Shares
Outstanding at January 1, 2020 (in shares) | shares	196,017
Granted (in shares) | shares	104,202
Vested/Converted (in shares) | shares	(32,242)
Forfeited (in shares) | shares	(37,049)
Outstanding at December 31, 2020 (in shares) | shares	230,928
Nonvested balance at end of period (in shares) | shares	177,855
Weighted-Average Grant-Date Fair Value per Share ($)
Outstanding at January 1, 2020 (in usd per share) | $ / shares	$ 42.21
Granted (in usd per share) | $ / shares	39.78
Vested/Converted (in usd per share) | $ / shares	41.19
Forfeited (in usd per share) | $ / shares	42.31
Outstanding at December 31, 2020 (in usd per share) | $ / shares	41.25
Nonvested balance at end of period (in usd per share) | $ / shares	$ 40.61