Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment, Net, by Type [Abstract]
Land & land improvements	$ 9,973	$ 9,959
Buildings	51,065	50,340
Furniture and equipment	38,172	35,939
Premises and equipment, gross	99,210	96,238
Less: Accumulated depreciation	(42,066)	(40,644)
Premises and equipment less depreciation, gross	57,144	55,594
Construction in progress	1,870	2,148
Total premises and equipment	$ 59,014	$ 57,742