Employee compensation plans - Schedule of Stock Compensation Assumptions Used (Details) - Stock Appreciation Rights (SARs)	12 Months Ended
	Dec. 31, 2021 USD ($)
January 6, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 days
Expected volatility factor (as a percent)	20.602%
Risk-free interest rate (as a percent)	0.002%
Quarterly dividends (in dollars per share)	$ 0.54
January 5, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	1 year
Expected volatility factor (as a percent)	35.942%
Risk-free interest rate (as a percent)	0.38%
Quarterly dividends (in dollars per share)	$ 0.54
January 11, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	2 years
Expected volatility factor (as a percent)	45.514%
Risk-free interest rate (as a percent)	0.738%
Quarterly dividends (in dollars per share)	$ 0.54
January 10, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	3 years
Expected volatility factor (as a percent)	39.569%
Risk-free interest rate (as a percent)	0.964%
Quarterly dividends (in dollars per share)	$ 0.54
January 11, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	4 years
Expected volatility factor (as a percent)	36.701%
Risk-free interest rate (as a percent)	1.164%
Quarterly dividends (in dollars per share)	$ 0.54