Premises and Equipment - Components of Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total cost	$ 100,626	$ 97,128
Less: accumulated depreciation	(44,990)	(40,452)
Net book value	55,636	56,676
Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Total cost	14,549	14,292
Premises and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total cost	55,703	54,158
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	$ 30,374	$ 28,678