Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Property, Plant and Equipment [Line Items]
Total	$ 603,155	$ 594,483
Accumulated depreciation	(112,939)	(108,571)
Premises and equipment, net	490,216	485,912	$ 453,603
Land [Member]
Property, Plant and Equipment [Line Items]
Total	79,314	79,231
Buildings [Member]
Property, Plant and Equipment [Line Items]
Total	372,231	365,102
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total	108,457	107,862
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total	$ 43,153	$ 42,288