Summary of changes in outstanding options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding	104,755
Options outstanding weighted avg exercise price	$ 37.93
Outstanding remaining term	4 years 9 months 17 days
Options exercisable, shares	96,586
Options exercisable, weighted avg exercise price	$ 37.26
Options exercisable remaining term	4 years 8 months 11 days
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding	104,755	120,089	132,504	147,538
Options outstanding weighted avg exercise price	$ 37.93	$ 35.33	$ 33.82	$ 33.48
Outstanding remaining term	4 years 9 months 17 days	5 years 3 months 18 days	5 years 9 months 17 days	6 years 8 months 11 days
Options outstanding, weighted avg grant date fair value	$ 1,416	$ 1,531	$ 1,631	$ 1,782
Options exercised, shares	(15,334)	(12,415)	(15,034)
Options exercised, weighted avg exercise price	$ 17.54	$ 19.23	$ 30.42
Options exercised, weighted avg grant date fair value	$ (115)	$ (100)	$ (151)
Options exercisable, shares	96,586
Options exercisable, weighted avg exercise price	$ 37.26
Options exercisable, weighted avg grant date fair value	$ 1,281
Options vested, shares	4,179
Options vested, weighted avg grant date fair value	$ 69