Premises and Equipment (Major Classifications) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,938,756	$ 1,859,822
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	800,325	726,778
Property, Plant and Equipment, Net	1,138,431	1,133,044
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	290,990	285,612
Premises and leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,158,699	1,130,650
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 489,067	$ 443,560