Parent Company Information (Components of Condensed Income Statement The Parent Company) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Income:
Loss on sale of investment securities									$ 0	$ 414	$ 609
Other non-interest income		$ 65,846	$ 64,551	$ 63,042	$ 70,617	$ 66,412	$ 65,075	$ 62,374
Operating Expense:
Compensation and benefits									359,926	332,127	297,517
Other non-interest expense									87,205	83,910	70,584
Income tax benefit	$ (17,029)	$ (30,281)	$ (29,090)	$ (21,951)	$ (23,845)	$ (24,445)	$ (24,599)	$ (23,434)	(98,351)	(96,323)	(93,032)
Parent Company [Member]
Operating Income:
Dividend income from bank subsidiary									120,000	145,000	110,000
Interest on securities and deposits									4,477	1,911	546
Loss on sale of investment securities									0	(2,410)	0
Alternative investments income									1,504	176	2,274
Other non-interest income									204	7,485	152
Total operating income									126,185	152,162	112,972
Operating Expense:
Interest expense on borrowings									10,380	9,981	9,665
Compensation and benefits									12,425	11,461	10,965
Other non-interest expense									10,583	6,278	6,005
Total operating expense									33,388	27,720	26,635
Income before income tax benefit and equity in undistributed earnings of subsidiaries and associated companies									92,797	124,442	86,337
Income tax benefit									3,004	3,086	2,929
Equity in undistributed earnings of subsidiaries and associated companies									159,638	79,599	115,463
Net income									$ 255,439	$ 207,127	$ 204,729