Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total	$ 594,483	$ 550,051
Accumulated depreciation	(108,571)	(91,977)
Premises and equipment, net	485,912	458,074
Land [Member]
Property, Plant and Equipment [Line Items]
Total	79,231	73,046
Buildings [Member]
Property, Plant and Equipment [Line Items]
Total	365,102	343,833
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total	107,862	94,254
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total	$ 42,288	$ 38,918