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Premises and Equipment - Major Categories of Banking Premises and Equipment and Accumulated Depreciation (Parenthetical) (Detail)
12 Months Ended
Dec. 31, 2019
Buildings [Member] | Minimum [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 15 years
Buildings [Member] | Maximum [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 39 years
Furnishings [Member] | Minimum [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 3 years
Furnishings [Member] | Maximum [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 15 years