Parent Company Information (Components of Condensed Income Statement The Parent Company) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Income:
(Loss) gain on sale of investment securities, net									$ 414	$ 609	$ 5,499
Other non-interest income	$ 70,617	$ 66,412	$ 65,075	$ 62,374	$ 59,679	$ 61,292	$ 59,245	$ 57,561
Operating Expense:
Compensation and benefits									331,726	297,517	270,151
Other non-interest expense									85,127	70,584	73,101
Income tax benefit	$ (23,845)	$ (24,445)	$ (24,599)	$ (23,434)	$ (23,627)	$ (24,995)	$ (20,426)	$ (23,984)	(96,323)	(93,032)	(91,973)
Parent Company [Member]
Operating Income:
Dividend income from bank subsidiary									145,000	110,000	100,000
Interest on securities and deposits									1,911	546	613
(Loss) gain on sale of investment securities, net									(2,410)	0	1,185
Alternative investments income									176	2,274	804
Other non-interest income									7,485	152	151
Total operating income									152,162	112,972	102,753
Operating Expense:
Interest expense on borrowings									9,981	9,665	10,041
Compensation and benefits									11,461	10,965	10,290
Other non-interest expense									6,278	6,005	4,562
Total operating expense									27,720	26,635	24,893
Income before income tax benefit and equity in undistributed earnings of subsidiaries and associated companies									124,442	86,337	77,860
Income tax benefit									3,086	2,929	8,798
Equity in undistributed earnings of subsidiaries and associated companies									79,599	115,463	113,068
Net income									$ 207,127	$ 204,729	$ 199,726