Premises and Equipment, Summary Composition (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 795,846		$ 795,846
Accumulated Depreciation	360,562		360,562
Net Book Value	435,284		435,284	$ 363,225
Land
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	69,649		69,649
Accumulated Depreciation	0		0
Net Book Value	69,649		69,649	67,737
Land improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	17,868		17,868
Accumulated Depreciation	8,513		8,513
Net Book Value	9,355		$ 9,355	7,212
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	394,191		$ 394,191
Accumulated Depreciation	163,833		163,833
Net Book Value	230,358		$ 230,358	212,536
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	47,291		$ 47,291
Accumulated Depreciation	34,049		34,049
Net Book Value	$ 13,242		$ 13,242	12,392
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]
Estimated Useful Lives	12 years	7 years
Cost	$ 176,023		$ 176,023
Accumulated Depreciation	122,681		122,681
Net Book Value	53,342		$ 53,342	49,891
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
Operating leases
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	53,982		$ 53,982
Accumulated Depreciation	8,602		8,602
Net Book Value	45,381		45,381	0
Leasehold improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	36,842		36,842
Accumulated Depreciation	22,884		22,884
Net Book Value	$ 13,958		$ 13,958	$ 13,457
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