Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Property, Plant and Equipment [Line Items]
Total	$ 609,431	$ 594,483
Accumulated depreciation	(115,950)	(108,571)
Premises and equipment, net	493,481	485,912	$ 449,304
Land [Member]
Property, Plant and Equipment [Line Items]
Total	79,521	79,231
Buildings [Member]
Property, Plant and Equipment [Line Items]
Total	379,808	365,102
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total	105,318	107,862
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total	$ 44,784	$ 42,288