Condensed Financial Information Of Parent Company Parent Company Information (Details 2) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net earnings	$ 84,037	$ 101,466	$ 93,647	$ 78,668	$ 357,818	$ 352,166	$ 299,619
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
(Increase) decrease in other assets					(118,477)	6,441	48,172
Loss (gain) on sale of securities, net					541	(9,485)	(3,744)
Tax effect included in stockholders' equity of restricted stock vesting					0	(4,406)	(841)
Earned stock compensation					25,568	23,319	15,630
Net cash provided by operating activities					483,968	581,107	593,878
Net Cash Provided by (Used in) Investing Activities [Abstract]
Cash acquired in acquisitions, net of cash consideration paid					160,318	0	260,936
Payments to Acquire Available-for-sale Securities					(1,298,105)	(375,261)	(992,680)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Tax effect of restricted stock vesting included in stockholders' equity					0	4,406	841
Restricted stock surrendered					9,476	5,313	8,400
Cash dividends paid, net					(247,403)	(243,437)	(215,110)
Net cash (used in) provided by financing activities					(537,942)	400,629	131,879
Cash and Cash Equivalents, at Carrying Value	398,437				398,437	419,670	396,486	$ 313,226
Supplemental Cash Flow Information [Abstract]
shares of unvested restricted stock, respectively)	1,305				1,305	1,228
Parent Only
Condensed Financial Statements, Captions [Line Items]
Net earnings					357,818	352,166	299,619
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
(Increase) decrease in other assets					(34,274)	96,668	145,709
Increase (Decrease) in Operating Liabilities					4,857	(17,311)	9,115
Loss (gain) on sale of securities, net					(15)	(405)	0
Tax effect included in stockholders' equity of restricted stock vesting					0	4,406	841
Earned stock compensation					25,568	23,319	14,994
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions					(83,260)	(100,956)	(91,198)
Net cash provided by operating activities					270,694	357,887	379,080
Net Cash Provided by (Used in) Investing Activities [Abstract]
Cash acquired in acquisitions, net of cash consideration paid					(223,818)	0	3,021
Payments to Acquire Available-for-sale Securities					426	995	0
Net Cash Provided by (Used in) Investing Activities, Continuing Operations					(223,392)	995	3,021
Net Cash Provided by (Used in) Financing Activities [Abstract]
Tax effect of restricted stock vesting included in stockholders' equity					0	(4,406)	(841)
Restricted stock surrendered					(109,153)	(33,244)	(8,400)
Increase (Decrease) in Notes Receivables					0	0	(50,000)
Cash dividends paid, net					(247,403)	(243,437)	(215,110)
Net cash (used in) provided by financing activities					(356,556)	(281,087)	(274,351)
Net Cash Provided by (Used in) Continuing Operations					(309,254)	77,795	107,750
Cash and Cash Equivalents, at Carrying Value	185,511				185,511	494,765	416,970	$ 309,220
Supplemental Cash Flow Information [Abstract]
shares of unvested restricted stock, respectively)	$ 446,233				$ 446,233	$ 0	$ 797,433