Premises and Equipment - Components of Premises and Equipment (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Gross premises and equipment		$ 111,862	$ 104,618
Less: Accumulated depreciation and amortization		(48,241)	(41,186)
Total premises and equipment, net		63,621	63,432
Land
Property, Plant and Equipment [Line Items]
Gross premises and equipment		16,604	16,875
Buildings, construction and improvements
Property, Plant and Equipment [Line Items]
Gross premises and equipment	[1]	$ 54,298	53,620
Buildings, construction and improvements | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, Estimated Useful Life in Years	[1]	2 years
Buildings, construction and improvements | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, Estimated Useful Life in Years	[1]	40 years
Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Gross premises and equipment		$ 70,902	70,495
Equipment
Property, Plant and Equipment [Line Items]
Gross premises and equipment		$ 40,960	$ 34,123
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, Estimated Useful Life in Years		3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, Estimated Useful Life in Years		10 years

[1] Leasehold improvements are depreciated over the lesser of the estimated useful life or the lease term.