Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net, by Type [Abstract]
Land & land improvements	$ 10,021	$ 9,522
Buildings	43,860	42,345
Furniture and equipment	34,530	31,428
Premises and equipment, gross	88,411	83,295
Less: Accumulated depreciation	(39,892)	(37,412)
Premises and equipment less depreciation, gross	48,519	45,883
Construction in progress	6,476	2,523
Total premises and equipment	$ 54,995	$ 48,406