Premises and Equipment, Net - Components of Premises and Equipment, Net (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 559,114	$ 528,316
Accumulated depreciation and amortization	(276,117)	(258,178)
Total premises and equipment, net	282,997	270,138
Land [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	73,734	66,620
Buildings [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	199,960	191,207
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	74,965	73,328
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 210,455	$ 197,161