Bank Premises and Equipment - Schedule of Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 89,672	$ 81,354
Accumulated depreciation and amortization	(50,610)	(47,402)
Total	39,062	33,952
Land [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	7,905	7,246
Bank Premises [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	34,556	28,175
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	34,381	33,259
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 12,830	$ 12,674
Minimum [Member] | Bank Premises [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	30 years
Minimum [Member] | Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	30 years
Maximum [Member] | Bank Premises [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	39 years
Maximum [Member] | Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	10 years
Maximum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	39 years