Bank Premises and Equipment - Schedule of Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 81,354	$ 68,271
Accumulated depreciation and amortization	(47,402)	(44,350)
Total	33,952	23,921
Land [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	7,246	3,850
Bank Premises [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	28,175	21,659
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	33,259	30,088
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 12,674	$ 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