Parent Company Information (Components of Condensed Income Statement The Parent Company) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Income:
Gain on sale of investment securities, net	$ 80	$ 0	$ 486	$ 43	$ 1,121	$ 42	$ 0	$ 4,336	$ 609	$ 5,499	$ 712
Other non-interest income	60,297	61,537	59,365	57,847	53,553	50,952	47,669	45,580
Operating Expense:
Compensation and benefits									297,517	270,151	264,835
Other non-interest expense									70,584	73,101	72,687
Income tax benefit	$ (24,146)	$ (25,075)	$ (20,663)	$ (24,092)	$ (23,753)	$ (23,824)	$ (23,159)	$ (21,237)	(93,976)	(91,973)	(77,113)
Parent Company [Member]
Operating Income:
Dividend income from bank subsidiary									110,000	100,000	90,000
Interest on securities and interest-bearing deposits									546	613	1,025
Gain on sale of investment securities, net									0	1,185	1,273
Alternative investments income (loss)									2,274	804	(392)
Other non-interest income									152	151	152
Total operating income									112,972	102,753	92,058
Operating Expense:
Interest expense on borrowings									9,665	10,041	7,273
Compensation and benefits									10,965	10,290	10,787
Other non-interest expense									6,005	4,562	5,966
Total operating expense									26,635	24,893	24,026
Income before income tax benefit and equity in undistributed earnings of subsidiaries and associated companies									86,337	77,860	68,032
Income tax benefit									2,929	8,798	9,742
Equity in undistributed earnings of subsidiaries and associated companies									117,074	113,068	101,682
Net income									$ 206,340	$ 199,726	$ 179,456