Bank Premises and Equipment and Leases - Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	$ 250,010	$ 247,739
Less allowance for depreciation and amortization	(153,366)	(152,494)
Bank premises and equipment, Net	96,644	95,245
Land [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	32,085	31,679
Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	105,759	103,014
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	40,789	41,001
Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	$ 71,377	$ 72,045