Bank Premises and Equipment - Components of Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 30,290	$ 28,983
Accumulated depreciation and amortization	(19,227)	(17,028)
Total	11,063	11,955
Leasehold improvements
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 14,080	14,028
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	3 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	25 years
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 7,110	6,447
Furniture, fixtures and equipment | Minimum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	5 years
Furniture, fixtures and equipment | Maximum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	10 years
IT equipment
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 8,645	8,002
IT equipment | Minimum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	3 years
IT equipment | Maximum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	5 years
Automobiles
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 455	$ 506
Automobiles | Minimum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	3 years
Automobiles | Maximum
Property, Plant and Equipment [Line Items]
Expected useful life (years)	5 years