Parent Company (Schedule of Condensed Financial Statements-Cash Flows) (Details) - USD ($) $ in Thousands		12 Months Ended
	May. 13, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Net income		$ 229,484	$ 237,951	$ 183,684
Adjustments to reconcile net income to net cash provided by operating activities
NET CASH PROVIDED BY OPERATING ACTIVITIES		313,700	284,637	309,366
Investing activities:
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES		(936,398)	(1,189,920)	641,219
Financing activities:
Proceeds from issuance of preferred stock		0	0	96,550
Cash dividends - common		(108,887)	(105,333)	(96,222)
Cash dividends - preferred		(5,876)	(5,876)	(5,337)
Purchase of treasury shares		(4,395)	(4,261)	(9,521)
Repurchase of common stock warrant	$ (12,200)	(12,150)	0	0
NET CASH PROVIDED (USED) BY FINANCING ACTIVITIES		389,091	684,885	(290,777)
(Decrease) increase in cash and cash equivalents		(233,607)	(220,398)	659,808
Cash and cash equivalents at beginning of year		697,424	917,822	258,014
Cash and cash equivalents at end of year		463,817	697,424	917,822
Parent
Operating activities:
Net income		229,484	237,951	183,684
Adjustments to reconcile net income to net cash provided by operating activities
Equity in undistributed income of subsidiaries		(143,149)	(175,161)	(121,829)
Decrease (increase) in Federal income tax receivable		4,863	35,672	(30,399)
Decrease (increase) in deferred Federal tax asset		1,776	(1,449)	27,032
Increase in interest payable		0	0	4,618
Other		(4,978)	(552)	924
NET CASH PROVIDED BY OPERATING ACTIVITIES		87,996	96,461	64,030
Investing activities:
Loans to subsidiaries		0	0	(50)
Repayment of loans to or investment in subsidiaries		0	110,675	0
Cash paid for acquisition, net of cash received		0	0	(315,069)
Sale of investment securities		0	784	0
Purchases of investment securities		0	(81)	(215)
NET CASH PROVIDED (USED) BY INVESTING ACTIVITIES		0	111,378	(315,334)
Financing activities:
Proceeds from issuance of subordinated debt		0	0	249,927
Proceeds from issuance of preferred stock		0	0	96,550
Repayment of long-term debt		0	(74,451)	0
Cash dividends - common		(108,887)	(105,333)	(96,222)
Cash dividends - preferred		(5,876)	(5,876)	(5,337)
Purchase of treasury shares		(4,395)	(4,261)	(9,521)
Repurchase of common stock warrant		(12,150)	0	0
NET CASH PROVIDED (USED) BY FINANCING ACTIVITIES		(131,308)	(189,921)	235,397
(Decrease) increase in cash and cash equivalents		(43,312)	17,918	(15,907)
Cash and cash equivalents at beginning of year		142,950	125,032	140,939
Cash and cash equivalents at end of year		$ 99,638	$ 142,950	$ 125,032