Premises and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 513,684	$ 488,311
Less: Accumulated depreciation and amortization	(290,882)	(270,505)
Premises and equipment, net	222,802	217,806
Land
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	35,560	36,097
Buildings and improvements
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	307,332	293,836
Furniture and equipment
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	150,876	137,282
Construction in progress
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 19,916	$ 21,096