Significant Accounting Policies (Premises and Equipment) (Detail)	12 Months Ended
	Dec. 31, 2017
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	40 years
Leasehold Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Leasehold Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	20 years
Furniture and Fixtures [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Furniture and Fixtures [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	10 years
Data Processing and Software [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	3 years
Data Processing and Software [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life (in years)	7 years