Employee compensation plans - Schedule of Stock Compensation Assumptions Used (Details) - Stock Appreciation Rights (SARs)	12 Months Ended
	Dec. 31, 2024
January 10, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	9 days
Expected volatility factor (as a percent)	22.353%
Risk-free interest rate (as a percent)	4.314%
January 11, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	1 year
Expected volatility factor (as a percent)	26.966%
Risk-free interest rate (as a percent)	4.183%
January 7, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	2 years
Expected volatility factor (as a percent)	24.353%
Risk-free interest rate (as a percent)	4.228%
January 6, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	3 years
Expected volatility factor (as a percent)	30.793%
Risk-free interest rate (as a percent)	4.261%
January 5, 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	4 years
Expected volatility factor (as a percent)	31.158%
Risk-free interest rate (as a percent)	4.319%