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Schedule of Number Restricted Stock Units and Performance Shares (Detail) - $ / shares
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Restricted Stock Units (RSUs)      
Share Based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average fair value at grant date $ 94.01 $ 69.58 $ 76.85
Outstanding at beginning of year 244,901 255,195 262,074
Granted 81,866 115,500 109,653
Shares issued (99,399) (105,750) (86,086)
Cancelled/Forfeited/Expired (9,100) (20,044) (30,446)
Outstanding at end of year 218,268 244,901 255,195
Performance Shares      
Share Based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average fair value at grant date $ 93.90 $ 69.86 $ 77.00
Outstanding at beginning of year 158,128 76,321 0
Change in performance conditions 44,385 23,998 12,530
Granted 74,427 75,940 66,542
Cancelled/Forfeited/Expired (8,859) (18,131) (2,751)
Outstanding at end of year 179,311 158,128 76,321