Premises and Equipment (Summary of Premises and Equipment) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land		$ 11,302		$ 12,595
Buildings and improvements		80,646		83,903
Leasehold improvements		82,067		83,971
Fixtures and equipment		76,665		76,146
Data processing and software		234,667		220,002
Total premises and equipment		485,347		476,617
Less: Accumulated depreciation and amortization		(355,346)		(339,204)
Premises and equipment, net		130,001		$ 137,413
Depreciation and amortization	$ 30,800	$ 33,100	$ 28,400