Condensed Financial Information Of Parent Company Parent Company Information (Details 2) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net earnings	$ 115,041	$ 116,287	$ 115,735	$ 118,276	$ 465,339	$ 357,818	$ 352,166
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Decrease (increase) in other assets					25,117	(118,477)	6,441
(Gain) loss on sale of securities, net					(8,176)	541	(9,485)
Tax effect included in stockholders' equity of restricted stock vesting					0	0	(4,406)
Earned stock compensation					29,768	25,568	23,319
Net cash provided by operating activities					608,027	483,968	581,107
Net Cash Provided by (Used in) Investing Activities [Abstract]
Cash acquired in acquisitions, net of cash consideration paid					0	160,318	0
Payments to Acquire Available-for-sale Securities					(1,180,545)	(1,298,105)	(375,261)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Tax effect of restricted stock vesting included in stockholders' equity					0	0	4,406
Restricted stock surrendered						9,476	5,313
Cash dividends paid, net					(288,193)	(247,403)	(243,437)
Net cash provided by (used in) financing activities					296,496	(537,942)	400,629
Cash and Cash Equivalents, at Carrying Value	385,767				385,767	398,437	419,670	$ 396,486
Supplemental Cash Flow Information [Abstract]
shares of unvested restricted stock, respectively)	1,251				1,251	1,305
Parent Only
Condensed Financial Statements, Captions [Line Items]
Net earnings					465,339	357,818	352,166
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Decrease (increase) in other assets					(36,362)	(34,274)	96,668
Increase (Decrease) in Operating Liabilities					(953)	4,857	(17,311)
(Gain) loss on sale of securities, net					0	(15)	(405)
Tax effect included in stockholders' equity of restricted stock vesting					0	0	4,406
Earned stock compensation					29,768	25,568	23,319
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions					217,663	(83,260)	(100,956)
Net cash provided by operating activities					675,455	270,694	357,887
Net Cash Provided by (Used in) Investing Activities [Abstract]
Cash acquired in acquisitions, net of cash consideration paid					0	(223,818)	0
Payments to Acquire Available-for-sale Securities					0	426	995
Net Cash Provided by (Used in) Investing Activities, Continuing Operations					0	(223,392)	995
Net Cash Provided by (Used in) Financing Activities [Abstract]
Tax effect of restricted stock vesting included in stockholders' equity					0	0	(4,406)
Restricted stock surrendered					(315,542)	(109,153)	(33,244)
Increase (Decrease) in Notes Receivables					(12,372)	0	0
Cash dividends paid, net					(288,193)	(247,403)	(243,437)
Net cash provided by (used in) financing activities					(616,107)	(356,556)	(281,087)
Net Cash Provided by (Used in) Continuing Operations					59,348	(309,254)	77,795
Cash and Cash Equivalents, at Carrying Value	244,859				244,859	185,511	494,765	$ 416,970
Supplemental Cash Flow Information [Abstract]
shares of unvested restricted stock, respectively)	$ 0				$ 0	$ 446,233	$ 0