Bank Premises and Equipment - Schedule of Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 61,823	$ 59,773
Accumulated depreciation and amortization	(38,406)	(35,667)
Total	23,417	24,106
Land [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	3,478	3,478
Bank Premises [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	19,272	19,272
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	26,271	24,131
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, gross	$ 12,802	$ 12,892
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