Parent Company Information (Components of Condensed Cash Flow The Parent Company) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net cash provided by operating activities	$ 380,549	$ 303,850	$ 469,408
Investing activities:
Alternative investments capital call	(12,244)	(6,065)	(1,215)
Net cash provided by (used for) investing activities	(2,288,609)	(2,549,756)	(1,317,924)
Financing activities:
Cash dividends paid to common shareholders	(144,965)	(140,783)	(114,959)
Cash dividends paid to preferred shareholders	(7,875)	(7,875)	(7,875)
Exercise of stock options	240	619	2,173
Common stock repurchased and acquired from stock compensation plan activity	(76,556)	(13,003)	(12,158)
Net cash (used for) provided by financing activities	1,913,269	2,174,302	921,229
Net (decrease) increase in cash and cash equivalents	5,209	(71,604)	72,713
Cash and cash equivalents at beginning of year	257,895	329,499	256,786
Cash and cash equivalents at end of year	263,104	257,895	329,499
Parent Company [Member]
Operating activities:
Net cash provided by operating activities	27,790	362,617	282,986
Investing activities:
Alternative investments capital call	(3,751)	(1,850)	0
Investment in subsidiaries	0	(296,000)	0
Net cash provided by (used for) investing activities	(3,751)	(297,850)	0
Financing activities:
Issuance of long-term debt	0	296,358	0
Cash dividends paid to common shareholders	144,967	140,783	114,959
Cash dividends paid to preferred shareholders	7,875	7,875	7,875
Exercise of stock options	240	619	2,173
Common stock repurchased and acquired from stock compensation plan activity	80,062	19,619	25,937
Net cash (used for) provided by financing activities	(232,664)	128,700	(146,598)
Net (decrease) increase in cash and cash equivalents	(208,625)	193,467	136,388
Cash and cash equivalents at beginning of year	510,940	317,473	181,085
Cash and cash equivalents at end of year	$ 302,315	$ 510,940	$ 317,473