Stock compensation plans - Weighted-average assumptions used to estimate fair value of non-vested shares granted (Detail) - Restricted Stock Units	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Weighted Average Fair Values [Line Items]
Risk-free interest rate	4.53%	1.57%	0.28%
Expected dividend yield	0.57%	0.42%	0.34%