Condensed Parent Company Financial Statements (Statements Of Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Expenses
Interest expense	$ 66,508	$ 57,399	$ 45,877	$ 36,123	$ 32,741	$ 31,700	$ 26,772	$ 23,179	$ 205,907	$ 114,392	$ 90,264
Salaries and employee benefits									480,077	430,078	405,158
(Loss) income before income taxes and equity in undistributed income of subsidiaries	107,662	122,814	121,591	108,066	95,785	104,248	101,946	88,018	460,133	389,997	331,854
Income tax benefit	(28,005)	(30,866)	(32,011)	(26,085)	(27,004)	(38,622)	(37,049)	(29,640)	(116,967)	(132,315)	(124,979)
Net income	$ 79,657	$ 91,948	$ 89,580	$ 81,981	$ 68,781	$ 65,626	$ 64,897	$ 58,378	343,166	257,682	206,875
Reportable Legal Entities | Parent Company
Income
Dividends and other revenue from subsidiaries									171,388	155,969	89,184
Other income									4	2,488	4,344
Total income									171,392	158,457	93,528
Expenses
Interest expense									22,375	19,207	18,498
Salaries and employee benefits									64,726	50,683	34,299
Other expenses									108,038	74,618	62,778
Total expenses									195,139	144,508	115,575
(Loss) income before income taxes and equity in undistributed income of subsidiaries									(23,747)	13,949	(22,047)
Income tax benefit									34,186	47,139	31,061
Income before equity in undistributed net income of subsidiaries									10,439	61,088	9,014
Equity in undistributed net income of subsidiaries									332,727	196,594	197,861
Net income									$ 343,166	$ 257,682	$ 206,875