Premises and Equipment - Summary of Premises and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Property, Plant and Equipment [Line Items]
Total	$ 548,964	$ 550,051
Accumulated depreciation	(99,660)	(91,977)
Premises and equipment, net	449,304	458,074	$ 413,933
Land [Member]
Property, Plant and Equipment [Line Items]
Total	70,628	73,046
Buildings [Member]
Property, Plant and Equipment [Line Items]
Total	339,378	343,833
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total	98,793	94,254
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total	$ 40,165	$ 38,918