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Employee Benefit Plans Summary of all Directors' Restricted Stock Activity (Detail) - Non Employee Director Restricted Equity Awards - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation cost related to unvested equity awards $ 1.0 $ 0.9 $ 0.9
Number of Shares      
Beginning of year 29,206 39,403 38,451
Add (deduct):      
Granted 30,439 29,206 39,403
Vested (29,206) (39,403) (38,451)
End of year 30,439 29,206 39,403
Weighted Average Grant Date Fair Value      
Beginning of year $ 105.16 $ 74.77 $ 73.43
Granted 109.75 105.16 74.77
Vested 105.16 74.77 73.43
End of year $ 109.75 $ 105.16 $ 74.77