Premises and Equipment, Summary Composition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 653,323
Accumulated Depreciation	322,360
Net Book Value	330,963	$ 330,315
Land
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	59,257
Accumulated Depreciation	0
Net Book Value	59,257	57,471
Land improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	13,115
Accumulated Depreciation	6,802
Net Book Value	$ 6,313	6,643
Land improvements | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	15 years
Land improvements | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years
Buildings and improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 341,947
Accumulated Depreciation	143,516
Net Book Value	$ 198,431	202,152
Buildings and improvements | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	39 years
Buildings and improvements | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	5 years
Computers
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 42,604
Accumulated Depreciation	31,526
Net Book Value	$ 11,078	9,051
Computers | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	5 years
Computers | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years
Furniture, fixtures and other equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 161,699
Accumulated Depreciation	119,650
Net Book Value	$ 42,049	42,549
Furniture, fixtures and other equipment | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	15 years
Furniture, fixtures and other equipment | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years
Leasehold improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 34,701
Accumulated Depreciation	20,866
Net Book Value	$ 13,835	$ 12,449
Leasehold improvements | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	15 years
Leasehold improvements | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Estimated Useful Lives	3 years