Bank Premises and Equipment - Summary of Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Land	$ 28,266	$ 29,050
Buildings	115,566	106,515
Furniture and equipment	58,145	54,353
Leasehold improvements	4,783	4,328
Gross	206,760	194,246
Less- accumulated depreciation and amortization	(84,075)	(78,534)
Total Bank Premises and Equipment	$ 122,685	$ 115,712
Minimum [Member] | Buildings [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years	20 years
Minimum [Member] | Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years	3 years
Minimum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years	5 years
Maximum [Member] | Buildings [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years		40 years
Maximum [Member] | Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years		10 years
Maximum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Life in years		15 years