Schedule of Number Restricted Stock Units and Performance Shares (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Restricted Stock Units (RSUs)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Weighted average fair value at grant date	$ 91.81	$ 87.56	$ 94.01
Outstanding at beginning of year	200,764	218,268	244,901
Granted	96,243	85,985	81,866
Shares issued	(94,055)	(84,848)	(99,399)
Cancelled/Forfeited/Expired	(12,986)	(18,641)	(9,100)
Outstanding at end of year	189,966	200,764	218,268
Performance Shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Weighted average fair value at grant date	$ 91.8	$ 88.05	$ 93.9
Outstanding at beginning of year	101,828	179,311	158,128
Granted	93,962	82,914	74,427
Change in performance conditions	18,211	69,924	44,385
Shares issued	(26,331)	(64,397)	0
Cancelled/Forfeited/Expired	(75,789)	(26,076)	(8,859)
Outstanding at end of year	111,881	101,828	179,311